Solve i̶n̶t̶e̶l̶l̶i̶g̶e̶n̶c̶e̶ ̶ coding, use it to solve everything else | Research @AnthropicAI | Past: RL @GoogleDeepmind: AlphaProof co-lead, Gemini.
San Francisco, CA
Joined July 2009
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Rishi Mehta retweeted
Anthropic has been warning about AI-enabled cyberattacks at least since 2022, with @logangraham at the forefront of that work. Back then, no VC was taking it seriously. The paradox is that risks only feel real once they’re legible, but waiting for incidents is too late. Anthropic also built sycophancy evals (@EthanJPerez et al.) a couple years before real-world incidents with ChatGPT made the risks of models excessively agreeing with users legible at scale. The lesson is to take early evidence of AI risks seriously before harm at scale makes them impossible to ignore.
Rishi Mehta retweeted
Claude Fable 5.1 is now available in Cursor!
It's the most capable model we’ve run on CursorBench 3.2, scoring 73.4% at max effort.
We found it especially skilled at verifying its own work, allowing it to take on difficult coding tasks from start to finish.
Rishi Mehta retweeted
Beginning July 20, Claude Fable 5 will be included in all Max and Team Premium plans, at 50% of limits.
Pro and Team Standard users will continue to have access to Fable via usage credits, and will receive a one-time $100 credit.
Demand for Fable has been challenging to predict, which is why we rolled it out to subscription plans in stages, extending access several times as we secured additional capacity.
Rishi Mehta retweeted
We’ve received notice that the Department of Commerce has lifted export controls on Claude Fable 5 and Mythos 5.
We'll begin restoring access tomorrow, and will share an update soon.
We’re grateful to our users for their patience, and to everyone who worked with us on redeploying the models.
Rishi Mehta retweeted
A bit of news: After nearly 9 years, I have decided to leave Google DeepMind and join Anthropic (after taking some time to recharge). I am incredibly grateful for my time at GDM. @demishassabis took a real chance letting me lead the AlphaFold team just six months after finishing my PhD, and the entire GDM team taught me so much about how to do great science. GDM is a special place, and I’ll still be excited to hear about what amazing things they discover next.
Rishi Mehta retweeted
The US government, citing national security authorities, has issued an export control directive to suspend all access to Fable 5 and Mythos 5 by any foreign national, whether inside or outside the United States, including foreign national Anthropic employees.
The net effect of this order is that we must abruptly disable Fable 5 and Mythos 5 for all our customers to ensure compliance.
Access to all other Claude models is not affected.
We apologize for this disruption to our customers. We believe this is a misunderstanding and are working to restore access as soon as possible.
Read our full statement: anthropic.com/news/fable-myt…
Rishi Mehta retweeted
After two days with Claude Fable 5 the best way I can describe it is "relentlessly proactive" - here's an example where I dropped in a screenshot of a bug and it span up custom CORS Python servers and used pyobjc-framework-Quartz to capture screenshots simonwillison.net/2026/Jun/1…
Rishi Mehta retweeted
We’re rolling out changes to make Fable 5’s safeguards for frontier LLM development visible.
Starting this week, flagged requests will visibly fall back to Opus 4.8—the same as our safeguards for cyber and bio. You will see this every time it happens. On the API, any flagged requests will return a reason for their refusal (coming to server-side fallback in the next few days).
We wanted to deploy Fable 5 to our users quickly and safely. Visible safeguards can be probed, so they have to be robust, which takes time to get right. Invisible safeguards can be targeted more narrowly, allowing us to ship quickly with very few false positives. We went with invisible safeguards for this reason—and that was the wrong tradeoff. You should have visibility into the safeguards we have in place, and why. We’re sorry for not getting the balance right.
Making the safeguards visible makes them easier to work around, so keeping them robust to jailbreaks will unfortunately mean more false positives while we improve the classifiers. We're also tuning our bio and cyber classifiers to trigger less often on harmless requests. We know this is frustrating and we’ll do our best to keep this period as short as possible.
If you think a request has been mistakenly flagged: run /feedback in Claude Code, click thumbs-down on the fallback in Claude.ai or Cowork, or file the safeguard appeal form for API requests. Your reports help us tune these classifiers and we appreciate your feedback.
support.claude.com/en/articl…
Rishi Mehta retweeted
Today I'm publishing a new essay, Policy on the AI Exponential. AI is progressing extremely fast—much faster than the policy process was built to handle. The essay lays out where I think the technology is now, and the action needed to close the gap: darioamodei.com/post/policy-…
Rishi Mehta retweeted
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 don't do this in prod!). The model still has quirks that people will run into and the safeguards are configured to be a little too trigger happy for launch, which can hopefully be tuned over time.
I feel a lot of things changing as working software increasingly comes out on a tap. The Jevon's paradox kicks in and I feel my own demand for software growing substantially. You can ask for anything - explainers, visualizers, dashboards, bespoke single-use apps (e.g. a full wandb that is hyper-specific just for your project), you can 10X your test suite, auto-optimize code, run giant research projects with custom HTML for the results, anything! "Free your mind" (Matrix ref). Really looking forward to all the things people build!
Fable 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.
ALT Benchmark table titled Mythos 5 & Fable 5, comparing Claude Mythos 5 and Fable 5 against Claude Mythos Preview, Claude Opus 4.8, GPT 5.5, and Gemini 3.1 Pro.
Rishi Mehta retweeted
at long last we have built and chosen not to release the zero-day machine from the classic sci-fi tale “please do not release the zero-day machine”
Rishi Mehta retweeted
In our investigation, we uncovered three separate bugs. They were partly overlapping, making diagnosis even trickier.
We've now resolved all three bugs and written a technical report on what happened, which you can find here: anthropic.com/engineering/a-…
Rishi Mehta retweeted
the openai IMO news hit me pretty heavy this weekend
i'm still in the acute phase of the impact, i think
i consider myself a professional mathematician (a characterization some actual professional mathematicians might take issue with, but my party my rules) and i don't think i can answer a single imo question
ok, yes, imo is its own little athletic subsection of math for which i have not trained, etc. etc., but. if i meet someone in the wild who has an IMO gold, i immediately update to "this person is much better at math than i am"
now a bunch of robots can do it. as someone who has a lot of their identity and their actual life built around "is good at math," it's a gut punch. it's a kind of dying.
like, one day you discover you can talk to dogs. it's fun and interesting so you do it more, learning the intricacies of their language and their deepest customs. you learn other people are surprised by what you can do. you have never quite fit in, but you learn people appreciate your ability and want you around to help them. the dogs appreciate you too, the only biped who really gets it. you assemble for yourself a kind of belonging. then one day you wake up and the universal dog translator is for sale at walmart for $4.99
the IMO result isn't news, exactly. in fact, if you look at the METR agent task length over time plot, i think agents being able to solve ~ 1.5 hour problems is coming right on time. so in some way we should not be surprised. and indeed, it appears multiple companies have achieved the same result. it's just... the rising tide rising as fast as it has been rising
of course, grief for my personal identity as a mathematician (and/or productive member of society) is the smallest part of this story
multiply that grief out by *every* mathematician, by every coder, maybe every knowledge worker, every artist... over the next few years... it's a slightly bigger story
and of course, beyond that, there is the fear of actual death, which perhaps i'll go into more later.
this package -- grief for relevance, grief for life, grief for what i have known -- isn't unique to the ai age or anything like that. i think it is a standard thing as one appreaches end of career or end of life. it just might be that that is coming a bit sooner for many of us, all at once.
i wonder if we are ready
Rishi Mehta retweeted
In early evaluations, the model soared in agentic scenarios—delivering up to a 10% improvement over the previous generation, driven by sharper tool use, tighter instruction-following, and stronger coding instincts. Additionally, Claude Opus 4 will be available on Copilot Enterprise and Pro+ plans.