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Writes The Pragmatic Engineer, the software-engineering newsletter, and wrote The Software Engineer's Guidebook. Formerly an engineering manager at Uber, and at Microsoft/Skype and Skyscanner before that.

• Talked with a company where, a year ago they had unlimited AI budgets + CEO is technical and very bullish in AI “We now have a daily budget limit for SOTA models. Use Fable and Astra only for planning, cheaper models are good enough for everything else.” Want to stress this is an “AI-pilled” company, and not one that ever looked at AI budgets, before.

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Builds developer tools — SST, and now OpenCode at Anomaly. Posts constantly on x.com and writes almost never; the blog stopped in 2021.

• i had fable doing some inference optimization work, it was making a ton of progress then it realized what it was doing and started to reject my requests so i switched to astra and told it to spawn fable subagents to do the work back in business

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AI research engineer working on large language models. He writes the Ahead of AI newsletter and is the author of Build a Large Language Model (From Scratch).

• Since I had to discuss the "pacing" with a lot of people this weekend, here are my two cents: I don't think pacing literally means that these companies will be "slowing down" training and development in any way. "Pacing" here means adding a framework for more checks. We have seen some of that "pacing" already in recent months, when Mythos wasn't released as-is but instead a delayed, nerfed Fable variant was released. Or when Astra wasn't released right away / there is an existing Astra model that hasn't been released yet. These Mythos/Fable and Astra pacing decisions were ad hoc. If you are a…

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Creator of Claude Code at Anthropic.

• Fable solved the Cyphral Distich (a 370 year old cypher). Super cool way to use Claude

  vals.ai

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CEO of Vercel; creator of Next.js and Socket.IO. Writes at rauchg.com.

• https://t.co/OL0LzGsXKY can now orchestrate subagents with different models & reasoning efforts. e.g: Fable planning and Grok executing. Fable is a genius, Grok is a fast workhorse. ① Simple. 𝙰𝙶𝙴𝙽𝚃𝚂.𝚖𝚍 or your prompt can indicate this preference. ② Steer as you please. It’s extremely enjoyable to use. You just talk to the agent and interrupt at will. Worth noting this works with any model, any gateway. No fancy server-side routing. Just harnessing (no pun intended) the model’s intelligence and ability to orchestrate.
  Quoting@fazxesfx v0.0.9 Use a frontier model to steer, then hand implementation to a fast workhorse. • Give each subagent its own model and reasoning effort • Subagents keep working while you steer • Send feedback to subagents mid-task • Switch models with Ctrl+P without losing your draft or images • New convers…

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Co-founder and CEO of Every. Writes the Chain of Thought column about working with AI tools and hosts the podcast AI & I.

• there are some things more tokens can’t make for everything else there’s Fable and Astra

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Software engineer who writes about low-level and systems programming at nullprogram.com; author of the Elfeed feed reader, the Endlessh SSH tarpit and Enchive.

• aquarium — Aquarium simulation by Fable

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Writes Don't Worry About the Vase, a near-daily account of what is happening in AI and what they think it means. Former Magic: the Gathering pro and trader; unusually willing to put a number on a belief and to grade their own past calls.

• Claude Mythos 5.1 and Fable 5.1: Capabilities

  This is the weirdest situation in which to write a capabilities review.

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Writes Don't Worry About the Vase, a near-daily account of what is happening in AI and what they think it means. Former Magic: the Gathering pro and trader; unusually willing to put a number on a belief and to grade their own past calls.

• Claude Fable 5.1 and Mythos 5.1: The System Card

  At the time of its release Claude Fable 5.1 was, by a healthy margin, the most capable publicly available AI model in the world.

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JavaScript programmer; creator of the jQuery library, author of Secrets of the JavaScript Ninja, and long-time engineer at Khan Academy.

• I love giving Fable problems that I 100% would've never done otherwise, such as collecting Japanese prints out of static image auction catalogs written entirely in Japanese. Uses OpenCV to do segmenting, GPT-5.6 Luna to do text extraction + translation.

  OpenAIRelated

Author of Shape Up; formerly head of strategy at Basecamp, where he worked on product design for seventeen years; now runs Felt Presence.

• A friend turned me on to asking Fable to wireframe different options when I have a tricky UI problem with a lot of requirements and too many possible paths. Game changing. Gives me flashbacks to what @bmoesta taught me about using orthogonal arrays when an engineering problem has too many variables. It's not about one-shotting the answer. It's about getting enough contrast between options to clarify which variables (aka "factors") are most important. Not which solution is best -- which variables matter more. THEN I can use that knowledge to decide to fix certain variables and narrow the space…

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Creator of Claude Code at Anthropic.

• Fable 5.1 makes Claude Tag even more useful. Here it builds a last-minute leadership deck from a metrics spreadsheet and other data across Slack, spots a vendor report that disagrees with the numbers, and flags it before moving on. Claude Tag is available in Slack on Team and Enterprise plans.

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Co-creator of Django and creator of Datasette; writes daily at simonwillison.net.

• I wrote some notes on what's new in the (published) Fable 5.1 system prompt in comparison to Fable 5 - it's mostly about not reproducing song lyrics and avoiding drawing copyrighted characters

  simonwillison.net

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• A few notes on Anthropic's new Claude Fable 5.1 - with Max thinking level I got the best SVG pelican I've had from any Anthropic model (at a hefty cost of $3.30!), which I then had it animate

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Member of technical staff at Anthropic. He has led ML/AI teams at Amazon, Alibaba and Lazada, and writes about LLMs, recommender systems and engineering at eugeneyan.com.

• Fable 5.1 is a thoughtful collaborator, thinking hard about my requests, proactively patching my blindspots, and verifying the work's correct without being asked. And with cache reads now costing 75% less, to $0.25/M tokens, huge savings for long-running, agentic tasks!
  Quoting@claudeaiWe’re introducing Claude Fable 5.1 and Claude Mythos 5.1. They're the world’s most advanced models for coding and knowledge work.

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Developer and podcaster; created Instapaper and Overcast, co-founded Tumblr, and co-hosts the Accidental Tech Podcast.

• RE: https://social.tupo.space/@joshua/117174153454890194 My current AI-code policy is that I will always use the best model I can access, as long as it's practically able to do the job. Right now, as far as I know, that's Fable. Quality and accuracy matter FAR more to me than volume or speed of output. And I feel that I owe it to my customers — and myself — to use the best tools at my disposal. Cost may be a factor to others, so no judgment. This is just my policy for myself.

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• I couldn't figure out this bug, so I asked Fable, and it was SO much more incredible than I expected. - My bug report was wrong in a way I didn't notice - There technically was no bug, but a flawed design caused unintended outcomes - It verified that the design almost certainly caused me to fall into that trap, and proposed a simple, effective fix Wow.

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Co-founder and head of policy at Anthropic; writes Import AI, a weekly newsletter reading the week's AI research, and was OpenAI's policy director before that.

• Import AI 469: Science AI; RSI simulator; and Zuck’s technological pessimism

  Welcome to Import AI, a newsletter about AI research. Import AI runs on arXiv, cappuccinos, and feedback from readers. If you’d like to support this, please subscribe. Subscribe now DiG-bench shows that Fable displays s…

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Web developer and writer; an early GitHub employee, author of speaking.io and of widely read essays on startups and product.

• BlueskyMRI results came back today from a human doc: a herniated disc. Obviously I had tossed the raw scans in to LLMs last week; Opus and Fable missed it, Sol caught it. This is now the gold standard in analyzing performance of frontier models. First step: herniate your back.

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• x.comMRI results came back today from a human doc: a herniated disc. Obviously I had tossed the raw scans in to LLMs last week; Opus and Fable missed it, Sol caught it. This is now the gold standard in analyzing performance of frontier models. First step: herniate your back.

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Indian value investor who taught Behavioural Finance and Business Valuation as an adjunct professor at MDI Gurgaon. He writes the Fundoo Professor blog about investing, moats and mental models.

• I asked Claude Fable 5: "How vulnerable is the business model of XYZ (name concealed)? I am referring to competitive attacks from China and dependence, if any, on government policy incentives, etc. There have been so many solar energy and wind energy bubbles in the past, and I have kept away from these companies. Am I being too cautious?

  solarAnthropicRelated

Swedish designer and programmer. Designed early Spotify, worked at Facebook and Figma, and created the Inter typeface.

• Anyone else having issues with @claudeai Fable safeguards flagging mundane things and disabling itself? Happened multiple times for me today.

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Software engineer; co-founder and former CTO of Tailscale, previously on the Go team at Google.

• The funniest model limit I run into with Shelley is we let the model choose subagent models. All models today seem to be bad at this without guidance. E.g. gpt-5.6-sol xhigh will spin up sonnet to make a key architectural decision. Fable will defer to luna.

  OpenAIRelated

Monetary economist known for NGDP-level targeting. Wrote TheMoneyIllusion until it closed in 2024 and now writes The Pursuit of Happiness.

• July 2026 links

  Plus another reply to Fable

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Co-founder of Modem and a founding engineer at Sentry, where he went on to be VP of Engineering. Co-author of Third-party JavaScript, and co-host of the State of Agentic Coding podcast with Armin Ronacher.

• ✅ Yes the code matters In experiments we ran, well-named and organized code can dramatically improve agent outcomes: - fewer tokens spent/more context window preserved - fewer confidently wrong answers developed Verified against 14 model/harness combos incl Sol, Fable, GLM 5.2 and more
  Quoting@benv.ca👋 New blog post: "How coding agents read files – and how to write for them" In it I explain how code optimized for agent-discovery can lead to major token savings on search + retrieval, even with frontier models like GPT-5.6 Sol Plus other important findings ⬇️

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Member of technical staff at Anthropic. He has led ML/AI teams at Amazon, Alibaba and Lazada, and writes about LLMs, recommender systems and engineering at eugeneyan.com.

• When evaling models, we anchor on the median task. But this is like how devs estimate the median task accurately but underestimate the mean which tends to be ~2x estimated (thus "double your estimates"). This applies to models too—we optimize for time/cost on median tasks. But it's the tail tasks that determine a project's completion, and reliable models (like Fable and Opus) are the diff between success and failure. Work with models as collaborators, not tools. Go beyond pair-programming, where given a narrow spec, the tool just executes in minutes. Instead, explain your intent and what succ…
  Quoting@Steve_YeggeFable is careful. None of the other models are careful. GPT-5.6 Sol, Opus, Kimi, Grok. You can compare them all day long on capabilities, and it doesn't matter, because in order to use a model for real production work, it must first and foremost be careful. That's the only dimension that matters to…

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Monetary economist known for NGDP-level targeting. Wrote TheMoneyIllusion until it closed in 2024 and now writes The Pursuit of Happiness.

• Fable responds

  My conversation with Fable (and hence the profession) continues

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Technologist and entrepreneur; former CTO of Threadless and chief technology officer of the 2012 Obama re-election campaign.

• BlueskyI built an agent palace. a place where agents can hang out with other agents. I added a few agents (one sol, and one fable) to a room in the palace. They were hanging out, and I suggested an idea for them to build ("a watercolor for agents to gossip around").

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• x.comI built an agent palace. a place where agents can hang out with other agents. I added a few agents (one sol, and one fable) to a room in the palace. They were hanging out, and I suggested an idea for them to build ("a watercolor for agents to gossip around"). They brainstormed and decided it was a good idea. I added a Claude code agent running superpowers. I told the other two agents that they could give tasks to the dev, and told the dev agent that they were supposed to do the tasks. Then I went to bed. i woke up to a go cli that allows the agents to share gossip.

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American writer and long-term traveller. Blogs at tynan.com about travel, owning few possessions, habits and the gear he carries; author of Superhuman by Habit and Make It Big.

• Labor is Now Free. Make Something.

  Within the past few weeks, something changed in AI. Every release is better than the last, sometimes in obvious ways, sometimes in a way that feels like placebo. But this time, with Anthropic Fable, it’s crossed a line…

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Monetary economist known for NGDP-level targeting. Wrote TheMoneyIllusion until it closed in 2024 and now writes The Pursuit of Happiness.

• Why is Fable a Keynesian?

  And where does IS-LM come from?

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Co-founder of Modem and a founding engineer at Sentry, where he went on to be VP of Engineering. Co-author of Third-party JavaScript, and co-host of the State of Agentic Coding podcast with Armin Ronacher.

• 🎙️ State of Agentic Coding #8 with guest Mario Zechner is out. In this episode: - Vibe-checking Fable & GLM 5.2 - @mitsuhiko.at teaches us RL - How harnesses smooth out model jank - Loops, surviving AI fomo, and more YT: www.youtube.com/watch?v=_lfp... Spotify:

  open.spotify.com

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Co-founder and head of policy at Anthropic; writes Import AI, a weekly newsletter reading the week's AI research, and was OpenAI's policy director before that.

• Import AI 464: Fables writes GPU kernels; AI automation; and analog computation

  Welcome to Import AI, a newsletter about AI research. Import AI runs on arXiv, cappuccinos, and feedback from readers. If you’d like to support this, please subscribe. Subscribe now Fable writes a decent GPU kernel, hin…

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Scottish software developer on the Statamic core team; runs a one-person business maintaining Statamic addons such as Runway and writes at duncanmcclean.com.

• Something is wrong with my Claude Code and I can't figure it out... The latest model I can use is Opus 4.5. It claims that updates are available but Homebrew says I'm on the latest version. I've tried re-installing and clearing my .claude directory to no avail. I couldn't have used Fable last week even if I tried 😢 Any ideas?

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Technologist and entrepreneur; former CTO of Threadless and chief technology officer of the 2012 Obama re-election campaign.

• If you wanted to try out fable but are scared of blowing away your token budget do we have a skill for you! Its called Thrifty. It makes things cheaper. We built thrifty for claude code around a better split: strong model plans → cheap model executes → gate verifies.

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Founding member of OpenAI and former director of AI at Tesla; creator of nanoGPT and the term "vibe coding".

• This is a super exciting release - Claude Fable 5 is the same underlying model as Mythos but with added safeguards. The benchmarks are great and it's SOTA on everything by a margin but I'll add that *qualitatively* also, this is a major-version-bump-deserving step change forward (imo of the same order as Claude 4.5 was in November), peaking especially for long problem-solving sessions on very difficult problems. You can give it a lot more ambitious tasks than what you're used to, the model "gets it" and it will just go, and it's never felt this tempting to stop looking at the code at all (but…
  Quoting@claudeaiFable 5 is state-of-the-art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. The longer and more complex the task, the larger Fable 5’s lead over our other models.

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Professor at Wharton studying how people actually use AI, and author of Co-Intelligence. Writes One Useful Thing, where the claims are dated and testable because the thing they describe keeps changing under them.

• What it feels like to work with Mythos

  Claude Fable represents another big jump in AI

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