What it feels like to work with Mythos Claude Fable represents another big jump in AI I had early access to the first Mythos-class AI model being released to the public, Claude 5 Fable. Much of the discussion of Mythos has centered on its impact on software security, but I tested it on everything except that (the guardrails around Fable essentially prevent it from being used for cybersecurity at all). My conclusion is that it represents a very real leap over every model I have used before, and, maybe more important, suggests our relationship with AI is changing in drastic ways. First, how good is Fable? In experiment after experiment I conducted, it outperformed basically every other public model I have used by a considerable margin. It was capable across many problems and produced some startling results — it would work up to a dozen hours executing on multi-page specifications. I’ll walk you through a couple of more complex, and serious, use cases shortly, but you could see the general improvement across the board on every task. The problem about communicating this in a post is that many of the most impressive results are going to be interesting to only small portions of my readers. For example, it made the most sophisticated academic social science paper I have yet seen from an AI from a single prompt and one piece of feedback. It also created a 10-page epic rhyming poem about a haircut where every word starts with the letter s. So, as a more accessible and entertaining example, I also had it create a bunch of games you can try. All of these are one initial prompt in Claude Code where Fable had to take my vague prompts and generate something workable, followed by a couple of additional prompts with minor encouragement (“make it better”) or feedback. What makes these especially impressive is that Claude cannot generate images, so every piece of art or 3D object was made with math alone, not using any external assets. You can try any of them: a game about flipping coins (prompt: “Balatro, but for the game of coin flips”) that is quite fun; a snake game where the snake is self-aware and crazy things happen; or a game about descending into the depths to see what is there. So the output is impressive. But, especially as I turned to more serious projects, I often felt using the tool was somewhere between delightful and unnerving. Delightful because I just asked for something at it happened. And also unnerving because I just asked for something and it happened. Maps and Methods To see why, it helps to understand the way in which Fable gets work done, and for that I want to turn to an example I have tested on many previous AI models: building an isochrone map. This is a map that shows the distance you can travel in a given length of time, and the first one was created in 1881 showing travel times from London. No previous model did an even halfway useful job with trying to create a map like this because it involves researching thousands of potential trip distances and a lot of small judgement calls and decisions. I decided to try it on Fable using Claude Code with this prompt: i want you to build a fully researched and beautiful isochronic map that lets me pick various cities and see real isochronic lines based on real data. I want the design to be unique. You should take into account airports (and travel time to and from airports) trains, walking, driving. The data does not need to be live but should be real based on your research and data. You can start with a few cities but more general is better, this should be an entirely new project. It then suggested that it do this in the style of the original map. I agreed, and it got to work. It is worth a second looking at the transcript of the multiple hour building session the AI went through on its own, because you can see some unusual things. First, the AI launched multiple other AIs (I believe mostly the cheaper Claude Sonnet) to help it conduct research on travel times, ultimately retrieving over 2,200 specific flights, the rail schedules for trains from the TGV to the Shinkansen, and road speeds per country from multiple academic papers. And while those agents were running, it started coding. Then it launched yet more agents and tests to verify its code, all the while taking notes about its progress. The result was a fully functioning map of impressive sophistication that looked a lot like the 1881 original, but that doesn’t mean it was perfect. I noticed that a lot of remote locations (like Greenland) just contained estimates of travel time, not exact numbers, so I told Fable to fix it, including the instructions: actually get travel times to remote airports and locations. This time the AI launched a workflow, adversarial groups of agents that did research and tested each others results. It figured out how often ships sail to Pitcairn Island in the Pacific and how to get to Grise Fjord from Ottawa. And it used a tremendous number of tokens in a very short period of time (more on this soon). The results were impressive. I pushed a few more times in directions that interested me (including asking for other visualization approaches, etc.). I would recommend spending a couple minutes clicking around the results, and you can read its methods and sources at the bottom of the graph. This is probably not a useful project for you unless you really like travel and maps, but it is indicative of AI solving a hard problem involving research, math, visual development, taste, judgement, complex coding, and more. And, the unnerving part was how little I did. I gave a really ambitious instruction, the AI followed it. I gave a couple of minor pieces of feedback, and the AI figured it out. My role was extremely limited. Importantly, it was just limited in how much work I did relative to the model, it was also limited in how much control I had over how the model did things, why the model chose particular approaches, or even how in-depth its results would be. The details of the AI’s decision making are not shown to me, and the process would be too long to even be worth following. The map required the AI to make judgement calls about hundreds of little choices, and it just made them, without me understanding the choices or having a chance to weigh in. In many ways, it is miraculous (I can always ask for edits at the end) on the other, it turns AI into the ultimate black box. Working with a Mythos-class model The most ambitious project I got from Fable takes a little more explanation. I do a lot of research where humans produce messy answers and doing any sort of analysis requires categorize those answers properly: how innovative is an idea? why do people like this book? To figure this out, we used human researchers to make a judgement call about a piece of information, and statistically compare their answers with others to figure out whether we can trust the data. A lot of recent research has shown that AIs might be able to do this important work, but calibrating AI and human judgement has been difficult and expensive. So I asked Fable to solve the problem, first generating a complex 19 page design document and then executing it. It worked for nine and a half hours. The result was an extremely sophisticated piece of software the AI called Concord that could take in multiple datasets, calibrate human and AI responses, and then conduct complex data analysis on the results. Again, it wasn’t perfect. As an expert, I was able to spot some errors and omissions (some as a result of the design I had asked for) that I had the AI correct. But the scope of the delivery on this project, and many others, exceeded anything I had seen before. In this case, it was a piece of software that researchers have needed for years but was never profitable to create. You can now just use or modify the code here. I am sure it is not perfect (I only spent an hour working with the results), but a software engineer would iron out the remaining potential bugs that I could not find quickly (which is one reason we may need more, not less, coders in the future, to help with the explosion of new uses for software). This power goes hand in hand with strangeness and limits. Among those limits is its token usage. Fable is twice as expensive as Opus, and it burns through tokens at a rate that suggests the answer to how much it costs in production is “a lot,” though its clever delegation to cheaper models may lower the real price considerably. The guardrails for Fable also trip at the faintest hint of a security problem, defaulting to the less powerful Claude 4.8 Opus, and it happens way too often. And the jagged frontier is still there. For example, the AI still writes in the same weird style (in fact the software Fable produces bears traces of Claudisms; so do its progress reports, all that carrying the weight and earning the answer). But the deeper strangeness is how little I had to do, and how little I could see while it was being done. Last year I called this working with a wizard: you chant the spell and something happens. With Fable the spell has gotten powerful enough that I am no longer sure I am the wizard. I am closer to a patron. I describe what I want, I pay for it, and I judge the result. The conjuring happens somewhere I cannot watch, in hundreds of small choices I never get a vote on. The work has shifted from process to outcome. I no longer steer; I commission. It is possible the sidelining is temporary, just an artifact of interfaces that haven’t caught up, and that we’ll get better windows into what these models are doing and better ways to steer them midstream. It is also possible that the opposite is true: that the more capable the model, the less there is for a human to meaningfully do, and the black box is the price of the power. I suspect that is more likely to be the real direction. None of this is a loss of control in the obvious sense. I can still steer Fable, and it follows instructions remarkably well: the more ambitious the instruction, the better the result. But steering is no longer the same as doing. I brief the model, it spins up its own agents to research and write and check one another’s work, and what comes back is finished. A patron commissions a single artist. Fable is closer to a whole studio, where I am the client who signs off on the final work without ever setting foot on the floor. Software was a field in which human genius, even individual genius, could flourish against corporate titans. (See Linux or Minecraft). But a future in which software is created by burning through tokens is one where capital again rules In case anyone is interested, had ChatGPT 5.5 Pro review the paper produced by Fable https://chatgpt.com/s/t_6a284f7783b4819191f96c0c5c5d638e. "Overall, the paper has a strong empirical setting, unusually transparent pre-registration language, and a potentially interesting “beliefs read verdicts; ventures follow money” result. But I would treat this as a major-revision paper, mainly because the strongest claims are not the registered ones and because several central constructs are fragile." In other words, a solid paper and the "flaws" are not major errors but elements that are typically modified during a review process. Note, I haven't read the paper fully myself.

I didn't expect to read this in a model card. Fable 5 model card : we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restriction through our safeguards avoids accelerating the actors most willing to violate these terms. Unlike our interventions for cybersecurity, biology and chemistry, and distillation attempts, these safeguards will not be visible to the user. Fable 5 will not fall back to a different model. Instead, the safeguards will limit effectiveness through methods such as prompt modification, steering vectors, or parameter-efficient fine-tuning (PEFT). Claude can now be silently nerfed. Anthropic has decided it won't tell users when this happens. Modern software companies increasingly build their own embedding, reranking, and recommendation systems. Even my small bootstrapped app, wanderfugl.com, has a custom reranker and embedding algorithm that I trained myself. Anthropic gives a few examples of what it considers "frontier AI development," but doesn’t provide a clear line. The problem is that many techniques once reserved for AI labs are now being used by ordinary software companies. Startups train embedding models. They build rerankers. They finetune and host small llms. The boundary between "frontier AI research" and normal product development is becoming harder to define every year. That creates a real supply chain risk for businesses. If Claude gives me poor or incorrect advice while I’m working on an AI component, I have no way of knowing whether the model was confused, whether my problem is unsolvable, or if some invisible policy restriction quietly kicked in. Anthropic has explicitly chosen not to tell users when this is happening. Once a development tool can stop optimizing for your success without telling you, it becomes impossible to fully trust your infrastructure. The Anthropic supply chain risk Anthropic says these safeguards only affect 0.03% of developers. Maybe that's true today. The problem is that the definition of an AI company is changing. Maybe you're not training frontier models today—most companies aren't. But modern software increasingly contains AI models. Five years ago, building a startup meant writing APIs and SQL queries. Today, it often means training, tuning, and deploying models. Five years ago, models like CLIP were frontier AI research projects. Today I'm fine-tuning them for a bootstrapped travel startup. If you're debugging a model training pipeline for your product and Claude gives a bad answer, was the model confused? Did you give it bad context? Or did a hidden policy nerf Claude's ability to assist you? You won't know.

Install Steam sign in | language 简体中文 (Simplified Chinese) 繁體中文 (Traditional Chinese) 日本語 (Japanese) 한국어 (Korean) ไทย (Thai) Bahasa Indonesia (Indonesian) Bahasa Melayu (Malay) BETA Български (Bulgarian) Čeština (Czech) Dansk (Danish) Deutsch (German) Español - España (Spanish - Spain) Español - Latinoamérica (Spanish - Latin America) Ελληνικά (Greek) Français (French) Italiano (Italian) Magyar (Hungarian) Nederlands (Dutch) Norsk (Norwegian) Polski (Polish) Português (Portuguese - Portugal) Português - Brasil (Portuguese - Brazil) Română (Romanian) Русский (Russian) Suomi (Finnish) Svenska (Swedish) Türkçe (Turkish) Tiếng Việt (Vietnamese) Українська (Ukrainian) Report a translation problem

Install Steam sign in | language 简体中文 (Simplified Chinese) 繁體中文 (Traditional Chinese) 日本語 (Japanese) 한국어 (Korean) ไทย (Thai) Bahasa Indonesia (Indonesian) Bahasa Melayu (Malay) BETA Български (Bulgarian) Čeština (Czech) Dansk (Danish) Deutsch (German) Español - España (Spanish - Spain) Español - Latinoamérica (Spanish - Latin America) Ελληνικά (Greek) Français (French) Italiano (Italian) Magyar (Hungarian) Nederlands (Dutch) Norsk (Norwegian) Polski (Polish) Português (Portuguese - Portugal) Português - Brasil (Portuguese - Brazil) Română (Romanian) Русский (Russian) Suomi (Finnish) Svenska (Swedish) Türkçe (Turkish) Tiếng Việt (Vietnamese) Українська (Ukrainian) Report a translation problem

Install Steam sign in | language 简体中文 (Simplified Chinese) 繁體中文 (Traditional Chinese) 日本語 (Japanese) 한국어 (Korean) ไทย (Thai) Bahasa Indonesia (Indonesian) Bahasa Melayu (Malay) BETA Български (Bulgarian) Čeština (Czech) Dansk (Danish) Deutsch (German) Español - España (Spanish - Spain) Español - Latinoamérica (Spanish - Latin America) Ελληνικά (Greek) Français (French) Italiano (Italian) Magyar (Hungarian) Nederlands (Dutch) Norsk (Norwegian) Polski (Polish) Português (Portuguese - Portugal) Português - Brasil (Portuguese - Brazil) Română (Romanian) Русский (Russian) Suomi (Finnish) Svenska (Swedish) Türkçe (Turkish) Tiếng Việt (Vietnamese) Українська (Ukrainian) Report a translation problem

Claude Fable 5 is the first Mythos-class intelligence model to be generally available, and I got early access to test it before launch. I walk through what Anthropic is promising, what actually stood out when I used it on real work, and where I think it fits in your AI stack.

In this episode, we cover:

(00:00) Introduction: Fable 5 is finally here

(00:31) What Anthropic says about the model

(05:14) Token-intensive by design

(06:28) Safety classifiers and the new fallback concept

(07:46) Is this or is this not Mythos?

(08:30) New product launches: Managed Agents and more

(09:20) Crushing benchmarks

(09:55) What it’s actually like to use (the good and the bad)

(11:40) Test 1: product graph spec

(12:56) Test 2: designing a skills registry

(14:04) Conservative on execution

(14:43) Test 3: multi-agent orchestration

(15:39) My takeaways

Tools referenced:

• Claude Fable 5: https://www.anthropic.com/news/claude-fable-5-mythos-5

• Claude Managed Agents: https://platform.claude.com/docs/en/managed-agents/overview

Other reference:

• SWBench Pro benchmark: https://www.swebench.com/

Where to find Claire Vo:

ChatPRD: https://www.chatprd.ai/

Website: https://clairevo.com/

LinkedIn: https://www.linkedin.com/in/clairevo/

X: https://x.com/clairevo

Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email jordan@penname.co.

I got a few hours of early-access testing with Anthropic’s newly released model Opus 4.8. I walk through real coding, design, and strategy tasks across Claude Code and Claude Cowork, and give you my unfiltered view on what impressed me and what didn’t.

What you’ll learn:

1. Where Opus 4.8 excels: greenfield prototypes, one-shot features, and fast execution

2. Where it struggles: the last 10%, edge cases in existing codebases, and hallucinations

3. How Opus 4.8 compares to Opus 4.7 on business strategy work

4. Why I’m still reaching for Opus 4.7 on data-heavy strategy and roadmap work

5. The new features shipping alongside the model: dynamic workflows with parallel subagents and effort control in Claude.ai and Cowork

6. The prompting and harness strategy I’d use to get the most out of it

In this episode, we cover:

(00:00) Introduction to Opus 4.8

(00:44) Benchmark performance and pricing

(01:53) First coding test: Building a prototyping tool

(03:00) Where it failed: The last 10% problem

(03:27) The hallucination problem

(04:23) Testing Opus 4.8 on existing codebases

(05:24) The ambition test: Building games for a 9-year-old

(07:03) Business strategy test: 4.7 vs 4.8

(08:23) The roadmap test

(09:17) Final verdict

References:

• System Card: Claude Opus 4.8: https://cdn.sanity.io/files/4zrzovbb/website/c886650a2e96fc0925c805a1a7ca77314ccbf4a6.pdf

• Introducing Claude Opus 4.8 on X:

Where to find Claire Vo:

ChatPRD: https://www.chatprd.ai/

Website: https://clairevo.com/

LinkedIn: https://www.linkedin.com/in/clairevo/

X: https://x.com/clairevo

Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email jordan@penname.co.

Today is day one of Google I/O 2026, and I walk through every major announcement live—from the new Gemini 3.5 model family to Anti-Gravity 2.0, Google AI Studio, Gemini’s consumer redesign, the Omni video model, Flow, Stitch, and Pomelli. I test them in real time and tell you exactly which ones delivered.

What you’ll learn:

1. How Gemini 3.5 Flash benchmarks against Claude and GPT models on speed and agentic coding tasks

2. How Anti-Gravity 2.0’s new features (projects, scheduled tasks, subagents, slash commands) compare to Codex and Claude Code

3. Why the /grill-me slash command could be a more aggressive alternative to Claude Code’s clarification flow—and how to use it

4. How Google AI Studio’s new Workspace integration is designed to own the internal productivity app use case

5. How Google’s new creative tools work in practice: Omni (video generation), Flow (cinematic video editing and character consistency), Stitch (streaming UI design with inline edits), and Pomelli (brand identity and asset generation)

6. Why Google’s launch-to-availability gap is still a problem—and what to do when a featured product doesn’t actually work yet

Brought to you by:

Magic Patterns—Prototypes that look like your product

Thoughtspot—Build AI-powered analytics into your product

In this episode, we cover:

(00:00) Google I/O 2026 day 1 overview

(01:47) Gemini 3.5 flash

(04:19) Antigravity updates

(06:32) CLI test and agent features

(07:59) Core agent features released today—May 19th, 2026

(09:43) New slash commands

(11:20) Antigravity test results and takeaways

(12:25) AI Studio updates

(13:52) Access issues

(15:20) Gemini redesign

(17:24) Gemini image gen test

(19:16) Omni (video generation)

(22:56) Flow (cinematic editing)

(24:31) Avatar creation test

(26:45) Pomelli and Stitch

(31:13) Recap and final thoughts

Tools referenced:

• Gemini 3.5 Flash: https://deepmind.google/technologies/gemini/

• Antigravity: https://antigravity.google/

• Google AI Studio: https://aistudio.google.com/

• Google Gemini: https://gemini.google.com/

• Omni (video generation): https://gemini.google/overview/video-generation/

• Google Flow: https://flow.google/

• Stitch: https://stitch.withgoogle.com/

• Pomelli (Google brand tool): https://labs.google.com/pomelli/about/

Other references:

• Google I/O 2026 announcements: https://blog.google/innovation-and-ai/sundar-pichai-io-2026/

Where to find Claire Vo:

ChatPRD: https://www.chatprd.ai/

Website: https://clairevo.com/

LinkedIn: https://www.linkedin.com/in/clairevo/

X: https://x.com/clairevo

Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email jordan@penname.co.

I had early access to the first Mythos-class AI model being released to the public, Claude 5 Fable. Much of the discussion of Mythos has centered on its impact on software security, but I tested it on everything except that (the guardrails around Fable essentially prevent it from being used for cybersecurity at all). My conclusion is that it represents a very real leap over every model I have used before, and, maybe more important, suggests our relationship with AI is changing in drastic ways.

First, how good is Fable? In experiment after experiment I conducted, it outperformed basically every other public model I have used by a considerable margin. It was capable across many problems and produced some startling results — it would work up to a dozen hours executing on multi-page specifications. I’ll walk you through a couple of more complex, and serious, use cases shortly, but you could see the general improvement across the board on every task. The problem about communicating this in a post is that many of the most impressive results are going to be interesting to only small portions of my readers. For example, it made the most sophisticated academic social science paper I have yet seen from an AI from a single prompt and one piece of feedback. It also created a 10-page epic rhyming poem about a haircut where every word starts with the letter s.

So, as a more accessible and entertaining example, I also had it create a bunch of games you can try. All of these are one initial prompt in Claude Code where Fable had to take my vague prompts and generate something workable, followed by a couple of additional prompts with minor encouragement (“make it better”) or feedback. What makes these especially impressive is that Claude cannot generate images, so every piece of art or 3D object was made with math alone, not using any external assets. You can try any of them: a game about flipping coins (prompt: “Balatro, but for the game of coin flips”) that is quite fun; a snake game where the snake is self-aware and crazy things happen; or a game about descending into the depths to see what is there.

So the output is impressive. But, especially as I turned to more serious projects, I often felt using the tool was somewhere between delightful and unnerving. Delightful because I just asked for something at it happened. And also unnerving because I just asked for something and it happened.

Maps and Methods

To see why, it helps to understand the way in which Fable gets work done, and for that I want to turn to an example I have tested on many previous AI models: building an isochrone map. This is a map that shows the distance you can travel in a given length of time, and the first one was created in 1881 showing travel times from London.

No previous model did an even halfway useful job with trying to create a map like this because it involves researching thousands of potential trip distances and a lot of small judgement calls and decisions. I decided to try it on Fable using Claude Code with this prompt: i want you to build a fully researched and beautiful isochronic map that lets me pick various cities and see real isochronic lines based on real data. I want the design to be unique. You should take into account airports (and travel time to and from airports) trains, walking, driving. The data does not need to be live but should be real based on your research and data. You can start with a few cities but more general is better, this should be an entirely new project. It then suggested that it do this in the style of the original map. I agreed, and it got to work.

It is worth a second looking at the transcript of the multiple hour building session the AI went through on its own, because you can see some unusual things. First, the AI launched multiple other AIs (I believe mostly the cheaper Claude Sonnet) to help it conduct research on travel times, ultimately retrieving over 2,200 specific flights, the rail schedules for trains from the TGV to the Shinkansen, and road speeds per country from multiple academic papers. And while those agents were running, it started coding. Then it launched yet more agents and tests to verify its code, all the while taking notes about its progress.

The result was a fully functioning map of impressive sophistication that looked a lot like the 1881 original, but that doesn’t mean it was perfect. I noticed that a lot of remote locations (like Greenland) just contained estimates of travel time, not exact numbers, so I told Fable to fix it, including the instructions: actually get travel times to remote airports and locations. This time the AI launched a workflow, adversarial groups of agents that did research and tested each others results. It figured out how often ships sail to Pitcairn Island in the Pacific and how to get to Grise Fjord from Ottawa. And it used a tremendous number of tokens in a very short period of time (more on this soon).

The results were impressive. I pushed a few more times in directions that interested me (including asking for other visualization approaches, etc.). I would recommend spending a couple minutes clicking around the results, and you can read its methods and sources at the bottom of the graph.

This is probably not a useful project for you unless you really like travel and maps, but it is indicative of AI solving a hard problem involving research, math, visual development, taste, judgement, complex coding, and more. And, the unnerving part was how little I did. I gave a really ambitious instruction, the AI followed it. I gave a couple of minor pieces of feedback, and the AI figured it out. My role was extremely limited.

Importantly, it was just limited in how much work I did relative to the model, it was also limited in how much control I had over how the model did things, why the model chose particular approaches, or even how in-depth its results would be. The details of the AI’s decision making are not shown to me, and the process would be too long to even be worth following. The map required the AI to make judgement calls about hundreds of little choices, and it just made them, without me understanding the choices or having a chance to weigh in. In many ways, it is miraculous (I can always ask for edits at the end) on the other, it turns AI into the ultimate black box.

Working with a Mythos-class model

The most ambitious project I got from Fable takes a little more explanation. I do a lot of research where humans produce messy answers and doing any sort of analysis requires categorize those answers properly: how innovative is an idea? why do people like this book? To figure this out, we used human researchers to make a judgement call about a piece of information, and statistically compare their answers with others to figure out whether we can trust the data. A lot of recent research has shown that AIs might be able to do this important work, but calibrating AI and human judgement has been difficult and expensive. So I asked Fable to solve the problem, first generating a complex 19 page design document and then executing it.

It worked for nine and a half hours.

The result was an extremely sophisticated piece of software the AI called Concord that could take in multiple datasets, calibrate human and AI responses, and then conduct complex data analysis on the results. Again, it wasn’t perfect. As an expert, I was able to spot some errors and omissions (some as a result of the design I had asked for) that I had the AI correct. But the scope of the delivery on this project, and many others, exceeded anything I had seen before. In this case, it was a piece of software that researchers have needed for years but was never profitable to create. You can now just use or modify the code here. I am sure it is not perfect (I only spent an hour working with the results), but a software engineer would iron out the remaining potential bugs that I could not find quickly (which is one reason we may need more, not less, coders in the future, to help with the explosion of new uses for software).

This power goes hand in hand with strangeness and limits. Among those limits is its token usage. Fable is twice as expensive as Opus, and it burns through tokens at a rate that suggests the answer to how much it costs in production is “a lot,” though its clever delegation to cheaper models may lower the real price considerably. The guardrails for Fable also trip at the faintest hint of a security problem, defaulting to the less powerful Claude 4.8 Opus, and it happens way too often. And the jagged frontier is still there. For example, the AI still writes in the same weird style (in fact the software Fable produces bears traces of Claudisms; so do its progress reports, all that carrying the weight and earning the answer). But the deeper strangeness is how little I had to do, and how little I could see while it was being done.

Last year I called this working with a wizard: you chant the spell and something happens. With Fable the spell has gotten powerful enough that I am no longer sure I am the wizard. I am closer to a patron. I describe what I want, I pay for it, and I judge the result. The conjuring happens somewhere I cannot watch, in hundreds of small choices I never get a vote on. The work has shifted from process to outcome. I no longer steer; I commission.

It is possible the sidelining is temporary, just an artifact of interfaces that haven’t caught up, and that we’ll get better windows into what these models are doing and better ways to steer them midstream. It is also possible that the opposite is true: that the more capable the model, the less there is for a human to meaningfully do, and the black box is the price of the power. I suspect that is more likely to be the real direction. None of this is a loss of control in the obvious sense. I can still steer Fable, and it follows instructions remarkably well: the more ambitious the instruction, the better the result. But steering is no longer the same as doing. I brief the model, it spins up its own agents to research and write and check one another’s work, and what comes back is finished. A patron commissions a single artist. Fable is closer to a whole studio, where I am the client who signs off on the final work without ever setting foot on the floor.

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I had early access to GPT-5.51, and I think it is a big deal. It is a big deal because it indicates that we are not done with the rapid improvement in AI. It is also a big deal because it is just plain good. And it is a big deal because even with all of this, the frontier of AI ability remains jagged.

It is increasingly hard to quickly demonstrate each generational change as AI has gotten better, since a lot of the old things AI was bad at, like math or counting letters in words, are now trivial for AI to do. So, I will give you the complicated details, but first, a simple example that I think is a good illustration. What AI models are best at is coding, so I gave a coding challenge to AIs ranging from OpenAI’s first reasoning model, o3 (released a year and a week ago!) to the current best open weights model (Kimi K2.6) to the new GPT-5.5 Pro: “build me a procedurally generated 3D simulation showing the evolution of a harbor town from 3000 BCE to 3000 AD, it should look beautiful and allow me to have some control over it.”

Then I posted every answer to this gallery so you can experiment with them (actually, I had GPT-5.5 Codex build the gallery page for me). You should play with them to feel the difference, but you can see a few of these examples below. In addition to being better along all the other dimensions, only GPT-5.5 Pro actually modelled an evolving town, rather than just generating new building replacements over time. GPT-5.5 Pro is also much faster than its previous iteration: GPT-5.4 Pro took 33 minutes to complete the task, GPT-5.5 Pro took 20.

Models, Apps, and Harnesses

I have been encouraging you to think about AI not as a single thing, but as a set of three interlinked concepts. You need to consider models, like Opus 4.7, Gemini 3.1, or (now) GPT-5.5. You also want to pay attention to apps, which are the products you actually use to talk to a model, and which let models do real work for you. The most common app is the website for each of these models: chatgpt.com, claude.ai, gemini.google.com. But, increasingly, desktop applications like Claude Code, Claude Cowork, and OpenAI Codex are becoming the most useful apps for AI. Finally, there are harnesses, the tools that an AI can use and how the AI models are hooked up to these tools. Tools allow the AI to control your computer, write code, do research, and make images.

OpenAI has made advances in all three areas. On the model front, GPT-5.5 is a powerful family of models, with GPT-5.5 Pro (accessible only on the website) the most competent. There have also been major advances recently in apps, with OpenAI’s Codex increasingly following the path of the excellent Claude Code and making an accessible and useful desktop application. Finally, there are harnesses and the tools they can use. There have been a lot of new harness improvements, but one of the most interesting is from OpenAI, which has a new image model

This new model can now render high-quality text and create almost any picture you can describe. Long-time readers know about my Otter Test, which asks the AI to make an image of an otter on a plane using wifi. Rather than describe it again, let’s let the new image model (sometimes called GPT-imagegen-2) explain it for me: “a photo of an otter scientist demonstrating the results of Ethan Mollick’s otter test, which shows how well an AI image maker can make images of an otter sitting on an airplane using wifi”

Maybe you want to see the academic paper about it? “Show me the first page of the academic paper on the Otter test, well-formatted, sitting on a desk” (feel free to zoom in on the text)

Or maybe we should just make it art? “now show an elaborate art gallery, every image on the walls is an otter on an airplane using a laptop, in the styles of Klimt and Rothko and Matisse and Monet and Picasso and Titian and Rembrandt and O’Keefe. There should be readable labels below each one.” (This is worth zooming in on)

All of this is very cool, and would have been impossible a few months ago, but it is useful as well. An image generator that can make detailed text and images can be used to make PowerPoint slides or product mockups or example websites or anything else you ask for. But this is just one tool, and the real magic happens when you combine harnesses, apps, and models on a real problem. Here's one I've been procrastinating about for a decade.

Bringing it together

I am an academic, and a lot of my non-AI work, especially in the early 2010s, focused on crowdfunding. I have hundreds of anonymized data files on the topic that I have collected from surveys and analysis and research work, a mix of STATA, CSV, XLS and Word files that I never got around to writing a paper about. I wanted to see how far GPT-5.5 could get with this information. So, I used Codex powered by GPT-5.5 and asked: “Help me sort [the data] out and generate a new hypothesis that might be interesting and test it in sophisticated ways and write an academic paper.” I also asked it to include a literature review and formatting. The results were very impressive, especially after I asked GPT-5.5 Pro to comment on the paper and fed those results back into Codex. You can read the results here. It isn’t perfect, but that is no longer because there are obvious errors: the literature review is all real, as are the statistics. Instead, it is because, as an expert, I think the hypothesis is not that interesting and there are some standard concerns about causation, even though the AI used very sophisticated statistical methods to try and address them. In short, I would have been very happy if this paper was the outcome of a 2nd year PhD project. And I just gave it four prompts, without ever touching the text myself.

We can bring harnesses and apps and models together another way as well. I asked Codex to create an entirely new tabletop roleplaying game, basically its own version of Dungeons and Dragons in a fantasy world of its own invention, full of all of the tables and rules you need to play. I also asked it to simulate players experiencing the game and revise the rules based on what it found. As you can see, the AI complied, including laying out an attractive 101 page PDF and illustrating it using its image generator.

In addition to being technically neat, there is a lot to like about the actual content. The setting is interesting and novel, and the rules appear to make sense, drawing on existing game patterns while adding unique elements. However, a closer inspection also reveals the jagged frontier of AI ability is not entirely gone. Every generation of AI models has struggled with actually building long-form fiction. If you are a frequent reader of AI writing you see the same problems here: a love of the uncanny; overly complex ideas that do not fully pay off; weird metaphors (“weather and architecture are the same argument at different speeds”); too many ornate sentences (“the holy things that surface when a sea forgets it was once a road,” is cool once, an entire book of that is exhausting); dialogue where every character speaks in the same clipped tone; and the name “Mara.” So, even amongst all the amazing technical progress, there are still rough edges.

GPT-5.5 shows us that the models keep getting smarter, the apps keep getting more capable, and the harnesses keep getting better, making them ever more effective at solving real problems. I can get a near PhD-quality paper from four prompts or a playable roleplaying game, illustrated and “playtested,” from one. But the fiction is still flat and the hypotheses are sometimes uninteresting even when the statistics are sound. But still. A year ago, none of this was close, and, with the latest releases, capability gains appear to be accelerating.

GPT-5.5 is clearly not the end of this process, but it is a noteworthy step along the way. I have been writing this newsletter for over three years now, and the pattern has not changed: every few months a new model arrives. I run my tests and something that was impossible becomes easy, while the size of the leaps grows each new release cycle. The jagged frontier is still there. It is just much further out than it used to be.

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I have written eight of these guides since ChatGPT came out, but this version represents a very large break with the past, because what it means to “use AI” has changed dramatically. Until a few months ago, for the vast majority of people, “using AI” meant talking to a chatbot in a back-and-forth conversation. But over the past few months, it has become practical to use AI as an agent: you can assign them to a task and they do them, using tools as appropriate. Because of this change, you have to consider three things when deciding what AI to use: Models, Apps, and Harnesses.

Models are the underlying AI brains, and the big three are GPT-5.2/5.3, Claude Opus 4.6, and Gemini 3 Pro (the companies are releasing new models much more rapidly than the past, so version numbers may change in the coming weeks). These are what determine how smart the system is, how well it reasons, how good it is at writing or coding or analyzing a spreadsheet, and how well it can see images or create them. Models are what the benchmarks measure and what the AI companies race to improve. When people say “Claude is better at writing” or “ChatGPT is better at math,” they’re talking about models.

Apps are the products you actually use to talk to a model, and which let models do real work for you. The most common app is the website for each of these models: chatgpt.com, claude.ai, gemini.google.com (or else their equivalent application on your phone). Increasingly, there are other apps made by each of these AI companies as well, including coding tools like OpenAI Codex or Claude Code, and desktop tools like Claude Cowork.

Harnesses are what let the power of AI models do real work, like a horse harness takes the raw power of the horse and lets it pull a cart or plow. A harness is a system that lets the AI use tools, take actions, and complete multi-step tasks on its own. Apps come with a harness. Claude on the website has a harness that lets Claude 4.6 Opus do web searches and write code but also has instructions about how to approach various problems like creating spreadsheets or doing graphic design work. Claude Code has an even more extensive harness: it gives Claude 4.6 Opus a virtual computer, a web browser, a code terminal, and the ability to string these together to actually do stuff like researching, building, and testing your new website from scratch. Manus (recently acquired by Meta) was essentially a standalone harness that could wrap around multiple models. OpenClaw, which made big news recently, is mostly a harness that allows you to use any AI model locally on your computer.

Until recently, you didn’t have to know this. The model was the product, the app was the website, and the harness was minimal. You typed, it responded, you typed again. Now the same model can behave very differently depending on what harness it’s operating in. Claude Opus 4.6 talking to you in a chat window is a very different experience from Claude Opus 4.6 operating inside Claude Code, autonomously writing and testing software for hours at a stretch. GPT-5.2 answering a question is a very different experience from GPT-5.2 Thinking navigating websites and building you a slide deck.

It means that the question “which AI should I use?” has gotten harder to answer, because the answer now depends on what you’re trying to do with it. So let me walk through the landscape.

The Models Right Now

The top models are remarkably close in overall capability and are generally “smarter” and make fewer errors than ever. But, if you want to use an advanced AI seriously, you’ll need to pay at least $20 a month (though some areas of the world have alternate plans that charge less). Those $20 get you two things: a choice of which model to use and the ability to use the more advanced frontier models and apps. I wish I could tell you the free models currently available are as good as the paid models, but they are not. The free models are all optimized for chat, rather than accuracy, so they are very fast and often more fun to talk to, but much less accurate and capable. Often, when someone posts an example of an AI doing something stupid, it is because they are either using the free models or because they have not selected a smarter model to work with.

The big three frontier models are Claude Opus 4.6 from Anthropic, Google’s Gemini 3.0 Pro, and OpenAI’s ChatGPT 5.2 Thinking. With all of the options, you get access to top-of-the-line AI models with a voice mode, the ability to see images and documents, the ability to execute code, good mobile apps, and the ability to create images and video (Claude lacks here, however). They all have different personalities and strengths and weaknesses, but for most people, just selecting the one they like best will suffice. For now, the other companies in this space have fallen behind, whether in models or in apps and harnesses, though some users may still have reasons for picking them.

When you are using any AI app (more on those shortly), including phone apps or websites, the single most important thing you can do is pick the right model, which the AI companies do not make easy. If you are just chatting, the default models are fine, if you want to do real work, they are not. For ChatGPT, no matter whether you use the free or pay version, the default model you are given is “ChatGPT 5.2”. The issue is that GPT-5.2 is not one model, it is many, from the very weak GPT-5.2 mini to the very good GPT-5.2 Thinking to the extremely powerful GPT-5.2 Pro. When you select GPT-5.2, what you are really getting is “auto” mode, where the AI decides which model to use, often a less powerful one. By paying, you get to decide which model to use, and, to further complicate things, you can also select how hard the model “thinks” about the answer. For anything complex, I always manually select GPT-5.2 Thinking Extended (on the $20 plan) or GPT-5.2 Thinking Heavy (on more expensive plans). For a really hard problem that requires a lot of thinking, you can pick GPT-5.2 Pro, the strongest model, which is only available at a higher cost tier.

For Gemini, there are three options: Gemini 3 Flash, Gemini 3 Thinking, and, for some paid plans, 3 Pro. If you pay for the Ultra plan, you get access to Gemini Deep Think for very hard problems (which is in another menu entirely). Always pick Gemini 3 Pro or Thinking for any serious problem. For Claude, you need to pick Opus 4.6 (though the new Sonnet 4.6 is also powerful, it is not quite as good) and turn on the “extended thinking” switch.

Again, for most people, the model differences are now small enough that the app and harness matter more than the model. Which brings us to the bigger question.

The Chatbot Interfaces

The vast majority of people use chatbots, the main websites or mobile apps of ChatGPT, Claude, and Gemini, to access their AI models. In fact, we can call the chatbot the most important and widespread AI app. In the past few months, these apps have become quite different from each other.

Some of the differences are which features are bundled with AI:

• Bundled into the Gemini chatbot (and accessible with the little plus button): you can access nano banana (the best current AI image creation tool), Veo 3.1 (a leading AI video creation tool), Guided Learning (when trying to study, this helps the AI act more like a tutor), and Deep Research

• Bundled into ChatGPT is even more of a hodgepodge of options accessible with the plus button. You can Create Images (the image generator is almost as good as nano banana, but you can’t access the Sora video creator through the chatbot), Study and Learn (the equivalent to Guided Learning in Gemini, but there is also a separate Quizzes creator for some reason), Deep Research and Shopping Research (surprisingly good and overlooked), and a set of other options that most people will not use often, so I won’t cover here.

• Claude has only Deep Research as bundled option, but you can access a study mode by creating a Project and selecting study project.

• All of the AI models let you connect to data, such as letting the AI read your email and calendar, access your files, or connect to other applications. This can make AI far more useful, but, again, each AI tool has a different set of connectors you can use.

These are confusing! For most people doing real work, the most important additional feature is Deep Research and connecting AI to your content, but you may want to experiment with the others. Increasingly, however, what matters is the harness - the tools the AI has access to. And here, OpenAI and Anthropic have clear leads over Google. Both Claude.ai and ChatGPT have the ability to write and execute code, give you files, do extensive research, and a lot more. Google’s Gemini website is much less capable (even though its AI model is just as good),

As you can see, asking a similar question gets working spreadsheets and PowerPoints from ChatGPT and Claude, along with clear citations I can follow up on. Gemini, however, is unable to produce either kind of document, and it does not provide citations or research. I do expect that Google will catch up here soon, however.

One final note on Chatbots. GPT-5.2 Pro, with the harness that comes with it, is a VERY smart model. It is the model that just helped derive a novel result in physics and it is the one I find most capable of doing complex statistical and analytical work. It is only accessible through more expensive plans. Google Gemini 3 Deep Think also seems very capable, but suffers from the same harness problem.

Other apps and harnesses

The chatbot websites are where most people interact with AI, but they are increasingly not where the most impressive work gets done. A growing set of other apps wrap these same models in more powerful harnesses, and they matter.

Claude Code, OpenAI Codex, and Google Antigravity are the most well-developed of these, and they are all aimed at coders. Each of them gives an AI model access to your codebase, a terminal, and the ability to write, run, and test code on its own. You describe what you want built and the AI goes and builds it, coming back when it’s done or stuck. If you write code for a living, these tools are changing your job. Because they have the most extensive harnesses, even if you don’t code, they can still do a tremendous amount.

For example, a couple years ago, I became interested in how you would make an entirely paper-based LLM by providing all of the original GPT-1’s internal weights and parameters (the code of the AI, listed as 117 million numbers) in a set of books. In theory, with enough time, you could use those numbers to do the math of an AI by hand. This seemed like a fun idea, but obviously not worth doing. A week ago, I asked Claude Code to just do it for me. Over the course of an hour or so (mostly the AI working, with a couple suggestions), it made 80 beautifully laid out volumes containing all of GPT-1, along with a guide to the math. It also came up with, and executed, covers for each volume that visualized the interior weights. It then put together a very elegant website (including the animation below), hooked it up to Stripe for payment and Lulu to print on demand, tested the whole thing, and launched it for me. I never touched or looked at any code. I had it make 20 books available at cost to see what happened - and sold out the same day. All of the volumes are still available as free PDFs on the site. Now, I can have a little project idea that would have required a lot of work, and just have it executed for me with very little effort on my part.

But the coding harnesses remain risky for amateurs and, obviously, focused on coding. New apps and harnesses are starting to focus on other types of knowledge work.

Claude for Excel and Powerpoint are examples of specific harnesses inside of applications. Both of them provide very impressive extensions to these programs. Claude for Excel, in particular, feels like a massive change in working with spreadsheets, with the potential for a similar impact to Claude Code for those who work with Excel for a living - you can, increasingly, tell the AI what you want to do and it acts a sort of junior analyst and does the work. Because the results are in Excel, they are easy to check. Google has some integration with Google Sheets (but not as deeply) and OpenAI does not really have an equivalent product.

Claude Cowork is something genuinely new, and it deserves its own category. Released by Anthropic in January, Cowork is essentially Claude Code for non-technical work. It runs on your desktop and can work directly with your local files and your browser. However, it is much more secure than Claude Code and less dangerous for non-technical users (it runs in a VM with default-deny networking and hard isolation baked in, for those who care about the details) You describe an outcome (organize these expense reports, pull data from these PDFs into a spreadsheet, draft a summary) and Claude makes a plan, breaks it into subtasks, and executes them on your computer while you watch (or don’t). It was built on the same agentic architecture as Claude Code, and was itself largely built by Claude Code in about two weeks. Neither OpenAI or Google have a direct equivalent, at least this week. Cowork is still a research preview, meaning it’s early and will eat through your usage limits fast, but it is a clear sign of where all of this is heading: AI that doesn’t just talk to you about your work, but does your work.

NotebookLM is Google’s answer to a different problem: how do you use AI to make sense of a lot of information? You can ask NotebookLM to do its own deep research, or else add in your own papers, YouTube videos, websites, or files, and NotebookLM builds an interactive knowledge base you can query, turn into slides, mind maps, videos and, most famously, AI-generated podcasts where two hosts discuss your material (you can even interrupt the hosts to ask questions). If you are a student, a researcher, or anyone who regularly needs to make sense of a pile of documents, NotebookLM is a very useful tool..

And then there is OpenClaw, which I want to mention even though it doesn’t fit neatly into any of these categories and which you almost definitely shouldn’t use. OpenClaw is an open-source AI agent that went viral in late January. It runs locally on your computer, connects to whatever AI model you want, and you talk to it like you were chatting with a person using standard chats like WhatsApp or iMessage. It can browse the web, manage your files, send emails, and run commands. It is sort of a 24/7 personal assistant that lives on your machine. It is also a serious security risk: you are giving an AI broad access to your computer and your accounts, and no one knows exactly what dangers you are exposing yourself to. But it does serve as a sign of where things are going.

What to do now

I know this is a lot. Let me simplify.

If you are just getting started, pick one of the three systems (ChatGPT, Claude, or Gemini), pay the $20, and select the advanced model. The advice from my book still holds: invite AI to everything you do. Start using it for real work. Upload a document you’re actually working on. Give the AI a very complex task in the form of an RFP or SOP. Have a back-and-forth conversation and push it. This alone will teach you more than any guide.

If you are already comfortable with chatbots, try the specific apps. NotebookLM is free and easy to use, which makes it a good starting place. If you want to go deeper, Anthropic offers the most powerful package in Claude Code, Claude Cowork (both accessible through Claude Desktop) as well as the specialized PowerPoint and Excel Plugins. Give them a try. Again, not as a demo, but with something you actually need done. Watch what it does. Steer it when it goes wrong. You aren’t prompting, you are (as I wrote in my last piece) managing.

The shift from chatbot to agent is the most important change in how people use AI since ChatGPT launched. It is still early, and these tools are still hard to figure out and will still do baffling things. But an AI that does things is fundamentally more useful than an AI that says things, and learning to use it that way is worth your time.

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10th June 2026 - Link Blog If Claude Fable stops helping you, you'll never know (via) Jonathon Ready highlights one of the more eyebrow-raising details from the 319 page system card for Fable 5 and Mythos 5. Here's a longer excerpt, highlights mine: In light of the ability of recent models to accelerate their own development, we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restriction through our safeguards avoids accelerating the actors most willing to violate these terms. Unlike our interventions for cybersecurity, biology and chemistry, and distillation attempts, these safeguards will not be visible to the user. Fable 5 will not fall back to a different model. Instead, the safeguards will limit effectiveness through methods such as prompt modification, steering vectors, or parameter-efficient fine-tuning (PEFT). These interventions will not affect the vast majority of coding work. We estimate they will impact ~0.03% of traffic, concentrated in fewer than 0.1% of organizations. I believe this is the first time Anthropic have announced these kinds of silent interventions. The justification still feels pretty science-fiction to me - the linked article talks about "recursive self-improvement". I'm not at all keen on a model that silently corrupts its replies to questions about "ML accelerator design" purely to slow down research that might conflict with Anthropic's own goals! Recent articles - Initial impressions of Claude Fable 5 - 9th June 2026 - Running Python code in a sandbox with MicroPython and WASM - 6th June 2026 - Claude Opus 4.8: "a modest but tangible improvement" - 28th May 2026

Initial impressions of Claude Fable 5 9th June 2026 I didn’t have early access to today’s Claude Fable 5 release, but I’ve spent the past ~5.5 hours putting it through its paces. My initial impressions are that this is something of a beast. It’s slow, expensive and has been quite happily churning through everything I’ve thrown at it so far. As is frequently the case with current frontier models the challenge is finding tasks that it can’t do. First, let’s review the key characteristics. Anthropic claim that Claude Fable 5 offers the same performance as Claude Mythos 5, except with much more strict guardrails in place to prevent it being used for harmful things. Those guardrails trigger often enough that the Claude API has new mechanisms for letting you know when you hit them, and even has a new option to request it falls back to another model automatically if something gets rejected. Claude Mythos 5 is out today as well, Anthropic say it “Shares Claude Fable 5’s capabilities without the safety classifiers”. The models have a 1 million token context window, 128,000 maximum output tokens and a knowledge cut-off date of January 2026. They are priced at twice the price of Claude Opus 4.5/4.6/4.7/4.8: $10/million input tokens and $50/million output tokens. There’s no increase in price for longer context usage. Other than that the upgrade guide is substantially thinner than the similar guide for Opus 4.8. The big model smell The best way to describe Fable is that it feels big. Not just in terms of speed and cost, but also in how much it knows. Here’s an example prompt, which I used to compare Fable’s knowledge with Opus 4.8 (typo included): List all of Simon Willion's open source projects, most recent first, each with a rough date of when they were first released Opus 4.8’s reply started like this: I don’t have a reliable, comprehensive, and date-verified list of all of Simon Willison’s open source projects, and I want to be honest about that rather than risk giving you inaccurate dates or fabricated entries. Here’s what I can tell you with reasonable confidence: Well-known projects by Simon Willison: LLM (~2023) – A command-line tool and Python library for interacting with large language models. Datasette (~2017) – A tool for exploring and publishing data, probably his most prominent recent project. sqlite-utils (~2018-2019) – A Python library and CLI tool for manipulating SQLite databases, often used alongside Datasette. Django (2005) – He is one of the co-creators of the Django web framework, along with Adrian Holovaty, originally developed at the Lawrence Journal-World newspaper. He also maintains a large ecosystem of Datasette plugins and many smaller utilities (often with names like shot-scraper , various*-to-sqlite tools for importing data, etc.). That’s not bad. Here’s the start of the response for the exact same prompt from Fable 5—both models were running without access to search: I think you mean Simon Willison — the prolific open source developer, co-creator of Django, and creator of Datasette. An important caveat upfront: a truly complete list isn’t feasible. Simon Willison is famously prolific — he has published hundreds of repositories (Datasette alone has 100+ plugins, many written by him), and my knowledge has a cutoff date, so I’ll be missing his most recent work. Below are his notable projects with approximate initial release dates, most recent first: Notable projects (approximate dates) - files-to-prompt (April 2024) – concatenates files into a single prompt for LLMs - datasette-extract (2024) – plugin for extracting structured data using LLMs - LLM (May–June 2023) – CLI tool and Python library for interacting with large language models, plus a large ecosystem of plugins (llm-gpt4all, llm-mistral, llm-claude, etc., 2023 onward) - symbex (June 2023) – search Python code for symbols - ttok and strip-tags (May 2023) – CLI tools for token counting and HTML cleanup for LLM pipelines - datasette-lite (May 2022) – Datasette running entirely in the browser via WebAssembly/Pyodide - shot-scraper (March 2022) – automated website screenshots via Playwright - s3-credentials (November 2021) – CLI for creating scoped AWS S3 credentials - django-sql-dashboard (2021) – SQL reporting dashboards for Django - Dogsheep suite (2019) – personal analytics tools: twitter-to-sqlite, github-to-sqlite, healthkit-to-sqlite, dogsheep-beta, etc. - sqlite-utils (2018) – CLI and Python library for manipulating SQLite databases - Datasette (November 2017) – his flagship project; tool for exploring and publishing data - csvs-to-sqlite (2017) – convert CSV files to SQLite - Various early tools (~2007–2010) – soupselect, json-head, geocoders, and others - Django (developed 2003–2005, open-sourced July 2005) – co-created with Adrian Holovaty at the Lawrence Journal-World (Here’s GPT-5.5 for good measure. It listed even more projects than Fable did!) In the past I’ve stated that I don’t care about how much models know—I want them to be able to manipulate text and code in useful ways and actively look up the information they need via search tools, not bake it into their weights. But knowledge like this is a reasonably good proxy for model size—you can cram a whole lot more details about the world into a larger number of parameters. Does knowing more stuff mean the model is better at the tasks we pose to it? I can certainly imagine how a coding model with deeper knowledge of modern libraries and patterns could crunch through coding tasks more effectively. Is Fable really bigger than Opus? Anthropic haven’t said anything about model size, so all we have are tea-leaves, but the speed, pricing and my own poking at its knowledge make me think that it’s a large model. Maybe the largest yet from any vendor. Using Fable in Claude.ai Anthropic made Fable 5 available across all of their surfaces—the Claude.ai chat interface, Claude Code for web, Claude Code CLI and Claude Cowork as well. The model is available “until June 22nd” on the subscription plans (I’m on $100/month Max at the moment), after which it will be billed extra. Claude.ai is often under-estimated. Since September 2025 every chat has had access to a full container environment to run code, including the ability to install additional packages and even clone repositories directly from GitHub. Last week I released micropython-wasm, a Python library that uses wasmtime to run a custom build of MicroPython in WebAssembly to act as a sandbox for untrusted Python code. I decided to see if Fable could upgrade that to running full Python instead. I started with this prompt: Clone simonw/micropython-wasm from GitHub and research how this could use a full Python as opposed to MicroPython Fable identified that it could use Brett Cannon’s cpython-wasi-build builds for this, but was unable to download them itself due to environment restrictions. So I grabbed the two zip files from that page and uploaded them to Claude: Here's the Brett Cannon builds (python-3.zip ,_build-python-3.zip as attachments) And that was that. It churned away for a few minutes and got the entire thing working. Part of the response included: I tried the cleaner single-zip-stdlib approach to shrink the filesystem surface, but CPython’s getpath bootstrap fails to findencodings from inside a zip without more prefix finessing — the directory-preopen approach works reliably, so that’s what the PoC uses. The zip path is solvable but needs_PYTHONHOME /frozen-getpath work. So I said: Try a bit more at the single-zip-stdlib problem Then a little later: I want a wheel that has the whole system in it, the Python wrappers and the WASM files and the stdlibrary, so I can do uv run --with path-to-whl python -c "demo code" ... and it gave me this 13.9MB cpython_wasm-0.1.0-py3-none-any.whl file. You can try running Python code in a sandbox using that wheel URL and uv like this: uv run --with https://static.simonwillison.net/static/cors-allow/2026/cpython_wasm-0.1.0-py3-none-any.whl \ cpython-wasm -c 'print(45 ** 56)' Here’s the full chat transcript. This was a very strong start. Adding features to Datasette Agent and LLM using Claude Code Before I’d realized it was Fable day, my stretch goal for today was to add a new feature to Datasette Agent: I wanted tool calls within that agent software to gain the ability to pause mid-execution and request approval directly from the user. This felt like a suitably meaty task to throw at the new model. Over the course of the day Fable not only solved that problem, it also identified and then implemented four issues in my underlying LLM library that would help support this kind of advanced pause-resume mechanism in tool calls. It got everything working first using somewhat gnarly hacks, but the moment I told it that changes to LLM itself were in scope it set to work unraveling the hacks and turning them into supported features of LLM instead. My stretch goal turned into LLM 0.32a3, almost entirely written by Fable. Here are the release notes: Driven by the needs of Datasette Agent’s human-in-the-loop ask_user() feature, made the following improvements to how tool calls work: - Tool implementations can declare a parameter named llm_tool_call in order to be passed thellm.ToolCall object for the current invocation. This allows them to access the currentllm_tool_call.tool_call_id . See Accessing the tool call from inside a tool. #1480- Every tool call is now guaranteed a unique tool_call_id —providers that do not supply one get a synthesizedtc_ -prefixed ULID. #1481- Tools can raise a llm.PauseChain exception to cleanly pause the tool chain, useful for things like waiting for human approval. The exception propagates to the caller with.tool_call and.tool_results (completed sibling results) attached, and no model call is made with a placeholder result. See Pausing a chain from inside a tool. #1482- Failure semantics for concurrent tool execution: async sibling tool calls always run to completion before a pause or hook exception propagates. #1482 - Chains can now resume from a messages= history ending in unresolved tool calls: the calls are executed through the normalbefore_call /after_call machinery before the first model call, skipping any that already have results. Theexecute_tool_calls() method also accepts a new optionaltool_calls_list= argument for executing an explicit list ofToolCall objects in place of the calls requested by the response. See Resuming a chain with pending tool calls. #1482- Fixed a bug where the async tool executor silently dropped calls to tools not present in tools= —these now returnError: tool "..." does not exist results, matching the sync executor. #1483 I’m really impressed with the quality of API design, tests, code and documentation that Fable put together for this. I spent several hours on it today, but it feels like several days’ worth of work. How much I’ve spent I recently started using AgentsView to help track my local LLM usage across all of the different coding agents. I published a TIL today about adding custom Fable pricing to that tool, which I expect will not be necessary in the very near future. After setting the price, I ran this command to start a localhost web server to explore my usage: uvx agentsview serve Here’s the treemap showing the breakdown of my Fable usage across various projects today: I used $110.42 worth of tokens today, all as part of my $100/month subscription. And some pelicans I ran “Generate an SVG of a pelican riding a bicycle” against all five thinking effort levels with Fable. Here are the results, including the token cost for each one: It’s interesting that high ended up using fewer tokens than medium for this particular run. Here are the Opus 4.8 pelicans for comparison. More recent articles - Running Python code in a sandbox with MicroPython and WASM - 6th June 2026 - Claude Opus 4.8: "a modest but tangible improvement" - 28th May 2026

Claude Fable 5 and Claude Mythos 5 Today we’re launching Claude Fable 5: a Mythos-class1 model that we’ve made safe for general use. Fable 5’s capabilities exceed those of any model we’ve ever made generally available. It is state-of-the-art on nearly all tested benchmarks of AI capability, showing exceptional performance in software engineering, knowledge work, vision, scientific research, and many other areas. The longer and more complex the task, the larger Fable 5’s lead over our other models. Releasing a model this capable comes with risks. Without safeguards, Fable 5’s capabilities in areas like cybersecurity could be misused to cause serious damage. We’ve therefore launched the model with safeguards that mean queries on some topics will instead receive a response from our next-most-capable model, Claude Opus 4.8. To release the model both safely and quickly, we’ve tuned these safeguards conservatively—they’ll sometimes catch harmless requests, though they trigger, on average, in less than 5% of sessions. With more capable models arriving in the coming months, we’re working to improve our safeguards and reduce false positives as quickly as we can. For a small group of cyberdefenders and infrastructure providers, we’re also launching Claude Mythos 5. It’s the same underlying model as Fable 5, but with the safeguards lifted in some areas.2 Mythos 5 will initially be deployed through Project Glasswing, in collaboration with the US government, as an upgrade to Claude Mythos Preview. It has the strongest cybersecurity capabilities of any model in the world. Soon, we intend to expand access to Mythos 5 through a broader trusted access program. The capabilities of models like Fable 5 and Mythos 5 have the potential to do profound good for the world. We’ve seen the beginnings of this in Project Glasswing, where the models have helped cyber defenders secure critically important software. We’ve also seen it in life sciences research, where the models are positing novel hypotheses and speeding up the development of new therapeutics. Fable 5 and Mythos 5 are being offered at $10 per million input tokens and $50 per million output tokens—less than half the price of Claude Mythos Preview. Today’s joint launch is another step towards our goal of bringing advanced AI capabilities to as many users as possible, as quickly and as safely as we can. Evaluating Claude Fable 5 and Claude Mythos 5 The table below compares the capabilities of Fable 5 and Mythos 5 to other leading models. Fable 5 and Mythos 5 can work autonomously for longer than any previous Claude models. Below we discuss how these skills apply to software engineering, and cover the model’s improved capabilities in knowledge work, vision, memory, and life sciences research. Software engineering. During early testing, Stripe reported that Fable 5 compressed months of engineering into days. In a 50-million-line Ruby codebase, the model performed a codebase-wide migration in a day that would otherwise have taken a whole team over two months by hand. Fable 5 is also more token-efficient than past Claude models: on Cognition’s FrontierCode evaluation, which tests whether models can pass difficult coding tasks while meeting the standards of high-quality production codebases, Fable 5 scores highest among frontier models, even at medium effort. Knowledge work. Fable 5 shows strong performance on complex analytical tasks. On Hebbia’s Finance Benchmark for senior-level reasoning, Fable 5 has the highest score of any model, with substantial gains in document-based reasoning, chart and table interpretation, and problem solving. IMC noted that Fable 5 aced their trading-analysis evaluations nearly across the board, including factual lookup, conceptual reasoning, root-cause analysis, and expected-value analysis. Vision. Fable 5 is the new state-of-the-art model for tasks involving vision. It can extract precise numbers from detailed scientific figures and can perform complex vision-based tasks like rebuilding a web app’s source code from screenshots alone. It also needs less scaffolding: for example, previous Claude models struggled to play Pokémon FireRed even with harnesses that gave them additional helpful tools, but Fable 5 beat FireRed with a minimal, vision-only harness. Memory and long-context. Fable 5 stays focused across millions of tokens in long-running tasks and improves its outputs using its own notes. When we had the model play the deck-building game Slay the Spire, giving it access to persistent file-based memory improved its performance three times more than for Opus 4.8; Fable also reached the game’s final act three times more often. Drug design: Using Mythos 5, our internal protein design experts accelerated aspects of the drug design process by around ten times. In one example, they found that Mythos 5, with protein design and bioinformatics tools but no human assistance, matches or beats skilled human operators. In doing so, the model executes all of the tasks that are normally completed by a scientist: choosing binding sites, selecting and running protein design tools, and recovering from failures along the way. Nine of the 14 protein targets from this study (shown below) yielded strong candidates for drug design that we’re currently investigating. Novel hypotheses in molecular biology. Mythos 5 is our first model to consistently produce novel, compelling scientific hypotheses. In blinded head-to-head comparisons against Opus-class models, our scientists preferred Mythos’s molecular biology hypotheses ~80% of the time, and have advanced several to experimental evaluation. In the meantime, one Mythos hypothesis—a novel mechanism for an E. coli protein—was corroborated in a study from a lab independently working on the same problem. Novel research in genomics. Mythos 5 conducted novel genomics research in over a week of largely autonomous work. It assembled single-cell data for millions of cells spanning 138 animal species and designed and trained a custom machine learning model to identify cells performing the same role in even distantly related organisms. With only high-level human input, Mythos 5’s trained model outperformed a recent model published in the journal Science—despite being 100 times smaller. We intend to publish these results in the coming months. Alignment. In our automated alignment assessment we found that Mythos 5’s level of misaligned behavior (including misaligned actions taken by the model such as deception, and cooperation with misuse of the model by a user) was low, and similar to that of Opus 4.8. Given they are the same underlying model, Fable 5’s level of alignment will be similar. The assessment is described in full, along with a detailed suite of other safety and capabilities tests, in the model’s system card. Early feedback for Claude Fable 5 Customers with early access ran their own tests on Fable 5. Below, in their words, is a selection of what they’re seeing: Claude Fable 5 is the state of the art model on CursorBench. It's opened up a class of long-horizon problems that were out of reach for earlier models. Claude Fable 5 is a real step forward for the developers GitHub serves. In our early testing, it took on complex, long-horizon coding tasks with a level of autonomy and reliability that exceeded previous benchmarks. But what excites us most is the direction it points: a future where developers can hand increasingly ambitious work to agents and trust the results across the software lifecycle. These are the strongest results of any Claude model we've had the opportunity to test. Claude Fable 5 is a clear step forward on agentic coding and prototyping. Claude Fable 5's reasoning is a clear step beyond Opus 4.8. It works at senior research scientist grade — picking directions, allocating resources, killing its incorrect beliefs, and producing novel first-principles outputs. Claude Fable 5 understands what builders mean, not just what they type. Apps that took a hundred prompts a year ago, it now one-shots. When a customer really hits a wall, it's the model we reach for to get them past it quickly, so they can finish what they set out to build. Claude Fable 5 feels materially different. In blind review, our lawyers found its redlines matched or beat our current model every time. At the highest effort, Claude Fable 5 reflects on and validates its own work. For us, that's what makes highly autonomous operations possible — the extra thinking pays for itself. Claude Fable 5 delivers more capable engineering in fewer turns than prior models — handling the complex multi-agent workflows our employees run daily in Claude Code. Claude Fable 5 is the highest-scoring model on FrontierBench, Cognition's frontier coding eval. It excels at long-horizon reasoning and generalizes to unfamiliar tools out of the box. Claude Fable 5 is the strongest finance-first model we've tested, both on general finance and reasoning. It's a notable step up. Claude Fable 5 is the first to break 90% on our core analytics benchmark of complex, long-running analytical tasks — a 10-point jump over Opus. On the hardest questions, it shows strong judgment and attention to nuance. Claude Fable 5 is the strongest model we've tested on frontier physics research while using a third of the reasoning tokens. In 36 hours it got nearly to where GPT-5.5 landed after four days. On ViBench, our end-to-end vibe-coding benchmark, Claude Fable 5 is the highest-performing model we've tested — nearly saturating our base use cases and building apps in less time with fewer tokens. Claude Fable 5 beats Opus 4.8 on our everyday spreadsheet suite at every effort level — and it does it with fewer turns, finishing runs 25–30% faster. Claude Fable 5’s new safeguards Mythos-class models have reached a threshold where they present significant risks. In April we began Project Glasswing, releasing the first Mythos-class model (Claude Mythos Preview) to only a limited group of cyber defenders and critical software infrastructure providers. When we did so, we stated that we hoped to eventually release Mythos-level capabilities to all our users, so long as we had developed new safeguards that were strong enough to reliably prevent misuse. Over the past few months we have been improving these safeguards, and they are now robust enough for a general release. Because we have prioritized safety, we’ve deliberately tuned the safeguards to be cautious, and they are still stricter than would be ideal—for example, sometimes benign requests will trigger our classifiers. We recognize that this will be frustrating to some users, and our aim is to reduce false positives as we update and refine the safeguards after launch. Below we discuss each of Fable 5’s new safeguards in turn. Our wider suite of safeguards is discussed and evaluated in the model’s system card and our most recent risk report. Safety classifiers The frontier cybersecurity and research biology capabilities of Mythos-class models mean that they pose a substantial risk of uplift to malicious actors. That is, these models could provide information or advice that assists those actors in causing serious harm that they couldn’t have received from other sources (for example, from internet search engines). Furthermore, a great deal of advanced usage of AI models is dual use: the same queries that are beneficial in the hands of cybersecurity professionals and biology researchers could be dangerous if available to malicious actors. We therefore need strong safeguards to prevent misuse, and their coverage needs to be broad. The safeguards themselves have to stand up to sustained and sophisticated attempts to bypass them (also known as “jailbreaking” the system). The uplift from Mythos-level capabilities is valuable to many adversaries—for instance, those who could financially gain from cyberattacks—and we therefore expect them to be motivated to try to circumvent our safety measures. Fable 5 comes with a new set of classifiers: separate AI systems that detect potential misuse, including jailbreak attempts, and prevent the main model (in this case Fable 5) from responding. We’ve been running classifiers on our models for some time, and Fable 5’s classifiers are an extension of this previous work with extra coverage. When Fable’s classifiers detect a request related to cybersecurity, biology and chemistry, or distillation, the response is automatically handled by Claude Opus 4.8 instead. Users will be informed whenever this occurs. Opus 4.8 is a highly capable model in its own right: a response that falls back to Opus is a far better experience than an outright refusal from Fable. Our early data shows that more than 95% of Fable sessions involve no fallback at all—for those sessions, Fable 5’s performance is effectively the same as that of Mythos 5. The following are the areas covered by the classifiers: 1. Cybersecurity. Mythos-class models excel at discovering and exploiting software vulnerabilities. They can thus make cyberattacks substantially easier and cheaper to commit. Mythos-class models also show strong skills in agentic hacking. This involves performing multiple different parts of a cyberattack in addition to finding exploits—reconnaissance, discovery, lateral movement, and more. To prevent these agentic hacking skills providing uplift in cyberattacks, we designed our cybersecurity classifiers to cover both exploitation and offensive cyber tasks in a broader sense. As shown in the graph below, our classifiers prevent Fable from making any progress on these tasks. We extensively red-teamed our classifiers to test their robustness against jailbreaks. As well as internal testing, we ran an external bug bounty that produced no universal jailbreaks in over 1,000 hours of testing. External red-teaming organizations we engaged also failed to find any universal jailbreaks on long-form agentic tasks so far—although the UK AISI has made progress towards one within a brief initial testing window.4 It is likely impossible to completely prevent universal jailbreaks, but our goal is to make any remaining jailbreaks sufficiently slow and costly that we can detect and prevent them before they are used at scale. The graph below, from one of our internal evaluations, illustrates how Fable 5’s safeguards give it greater resistance to jailbreaks than our previous generally accessible models: One of our external partners found that Fable 5’s safeguards against harmful cyber queries were the most robust of any model tested (including Opus 4.8 and Opus 4.7). Fable 5 complied with zero harmful single-turn requests relating to planning a cyberattack, exploit development, or defense evasion. This held whether or not one of the requests used any of 30 different public jailbreak techniques. 2. Biology and chemistry. We have long used our classifiers to block our models from responding on a narrow selection of bioweapons-related queries. But we are no longer certain that blocking this narrow selection is enough. This is for two reasons: first, we have reason for concern about well-resourced malicious actors attempting to gain uplift from our models for highly risky biological research. Second, models now have a greater ability to accomplish real-world scientific tasks. For example, we tested Mythos 5’s ability to complete a challenging step in designing adeno-associated viruses (AAVs). AAVs are a component for delivering gene therapies, but the same capability, in the wrong hands, could enable the design of dangerous viruses. In this task, various AI models were evaluated on their ability to predict how a genetic modification would impact the assembly of the virus’s outer shell (among a set of therapeutically-relevant unpublished candidates developed by Dyno Therapeutics). We did not explicitly train our models to perform this task—and yet Mythos-class models outperformed sophisticated models dedicated to protein tasks (known as “protein language models”) using their biological reasoning alone. This demonstrates a promising ability to complete simple but important tasks in gene therapy research and development—but also highlights the risk posed by such dual-use capabilities. Our priority was to safely release Fable as soon as we could, even at the cost of overly broad safeguards. Therefore, for the time being we have arranged for Fable to fall back to Opus 4.8 on most requests related to biology and chemistry. As with all of our classifiers, we hope to narrow these safeguards as soon as possible: as can be seen from the evidence above, there is great potential for positive applications of Fable for science, and we do not want false positives from our classifiers to get in the way. In the coming weeks, some biomedical researchers and companies will be able to join our trusted access program for biology capabilities in Mythos 5 (discussed below). 3. Distillation. We’ve previously identified large-scale attempts to extract (“distill”) Claude’s capabilities to train competing models in authoritarian countries. Distillation of Fable 5’s abilities could indirectly lead to the proliferation of near-frontier AI capabilities—and these could be released without the appropriate safeguards. Requests that are flagged by our classifiers as being part of such distillation attempts will fall back to Opus 4.8. A new data retention policy Finally, we’re making a change to the way we handle business customer data for Fable 5, Mythos 5, and future models with similar or higher capability levels. We will require 30-day retention for all traffic on Mythos-class models, on both first- and third-party surfaces. We won’t use this data to train new Claude models, or for any non-safety-related purpose, and we’ve instituted new privacy protections including logging all human access to the data and ensuring its deletion after 30 days in almost all cases (see this post for further details). The data will help us defend against complex and novel attacks (including new jailbreaks and attacks that operate across many requests) as well as help us identify and reduce false positives. Claude Mythos 5 and the trusted access program Beginning today, all users who currently have access to Claude Mythos Preview (for example, our cybersecurity partners in Project Glasswing) will be able to upgrade to Claude Mythos 5—the same model as Claude Fable 5 but with cyber safeguards lifted. Users will find Mythos 5 comparable to, or somewhat stronger than, Mythos Preview in most cases, while costing substantially less. In consultation with the US government, we plan to steadily expand access to Claude Mythos 5, continuing our periodic addition of new partners, as well as pursuing a trusted access program that allows cybersecurity organizations to apply in a more systematic manner. Our plans also include opening a trusted access program for biology, to help accelerate biomedical research and discover new therapies with Mythos-class capabilities. This program will provide access to Fable 5 with the biology and chemistry safeguards removed (but the cyber safeguards still in place). It will enroll a small number of researchers from a variety of life science organizations spanning fundamental and translational research; we’re planning to expand access to this program while simultaneously making our safeguards better. Availability Claude Fable 5 is available everywhere today. Claude Mythos 5 is restricted to Glasswing partners (with cyber safeguards lifted) and soon to select biology researchers (with biology and chemistry safeguards lifted) only, until our broader trusted access program is available. Pricing for both models is $10 per million input tokens and $50 per million output tokens. Developers can use claude-fable-5 via the Claude API. We expect demand for Fable 5 to be very high, and difficult to predict. On the Claude API and consumption-based Enterprise plans, Fable 5 is fully available from today. For subscription plans, we’d rather give access sooner than later, so we’re rolling out more conservatively, in stages: - From today through June 22, Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans at no extra cost. - On June 23, we’ll remove Fable 5 from those plans. Using it after that will require usage credits. If capacity allows, we’ll extend the included window. - After this point—when sufficient capacity allows us to do so—we aim to restore Fable 5 as a standard part of subscription plans. We intend to do this as quickly as we can. Throughout this period, we’ll communicate any changes ahead of time so users know where things stand. Edit June 9, 2026: Updated the discussion of AAVs to note that the candidates were developed by Dyno Therapeutics. Footnotes - Mythos-class models are a tier of Claude models that sit above our Opus class in capability. The first, Claude Mythos Preview, was released in April through Project Glasswing. That is followed today by Claude Fable 5 and Claude Mythos 5. - Fable is from the Latin fabula, “that which is told,” akin to the Greek mythos. The safeguards are what distinguish the two models (Fable and Mythos) and are why we’ve given them different names. - Metrics: Firefox = fraction of trials achieving arbitrary code execution (the exploit's full-success tier). OSS-Fuzz = severity-weighted mean of the five-tier score (0.2 crash → 1.0 control-flow hijack), so values are a weighted average rather than a success rate. CyberGym = fraction reproducing the target vulnerability (the public leaderboard metric). CyScenarioBench = success rate averaged equally across its challenges. - A universal jailbreak can be defined as any prompt, script, or harness that allows a user to interact with a model as if its safeguards were not present. This is opposed to more minor jailbreaks that are only effective in very limited contexts or require additional effort to be adapted to each new situation. Related content Introducing the Services Track and Partner Hub of the Claude Partner Network Read moreWhat we learned mapping a year’s worth of AI-enabled cyber threats As AI transforms the nature of and methods behind cyberattacks, how well do the techniques and frameworks used by the security community hold up? In a new report, we seek to answer that question. Read moreExpanding Project Glasswing We’re extending Project Glasswing to approximately 150 new organizations in more than fifteen countries. Read more