Thrilled to share that I have joined @AnthropicAI as a life science researcher! I am confident that Claude will do amazing things to accelerate biology. Big things ahead!

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…

I know this is frustrating. As we said at launch, Fable blocks bio requests entirely for now and reroutes them to Opus 4.8. We made this tradeoff in order to get the model out safely and quickly while we work to refine the classifiers. It is absolutely our goal to enable the whole bio community to use our most powerful models, with appropriately scoped protections in place. We’re working towards this as fast as possible.

AI is advancing at a pace our policymaking institutions were never built for—and the gap between the two is becoming the central challenge of the technology. In his latest essay, our CEO Dario Amodei lays out how to close it. We're launching three new initiatives to support the efforts he outlines.

Sign up for Mythos 5 access updates: claude.com/form/mythos-acces…

Fable 5 is the best model I've ever used. I’ve been spending most of my time in the last few months helping to bring Mythos-level models to general availability safely. These models changed everything. So stoked that anyone can use Fable today! Can't wait to see what you all build with it.

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!

This is THE model we use, excited to share the magic.

My favorite chart from our system card - FrontierCode is an excellent eval, and it accurately reflects the step up I feel when using Fable!

I wrote up some thoughts on AI agents and biological databases for the @AnthropicAI Science blog. 🚗🧬 Based on research with @ferbsx and @PardisSabeti

Our internal data shows Claude is accelerating AI development—a possible path to recursive self-improvement, or AI autonomously building a more capable successor. It’s happening faster than we thought, and the implications deserve greater attention. anthropic.com/institute/recu…

Opus 4.8 is almost as good as Claude Mythos in most of biology benchmarks! 🔥🔥

Excited to release Opus 4.8 today! We heard your feedback on 4.7 and have made many fixes for 4.8. 4.8 understands nuances better, feels much more natural to talk to, and is overall a stronger collaborator on everything from coding to knowledge work.

With the help of Claude Mythos Preview, the Firefox team fixed more security bugs in April than in the past 15 months combined.

"We anticipate that bridge recombinases, together with advances in predictive bRNA design and bacterial delivery systems, will form a foundation for “synthetic microbiomics”, the systematic, programmable orchestration of gene flow within complex microbial ecosystems."

One of the many amazing parts of this paper that you might have missed at first glance!

Pioneering work from the @bradyfcress lab using bridge recombinases to perform programmable genomic rearrangements in diverse species (multiple phyla). Congrats to @jayman14661, @swartz_sophi, Agnès Oromí-Bosch, and team!

From @bradyfcress revolutionary work!