I've been on a Blender kick with Opus 5.5. Its better 3D modeling and vision mean you can build an entire world from a single prompt. Historically accurate San Francisco Market street in 1906, pre-earthquake

Worth spending a few minutes this weekend to read this essay in full. Embedded evaluators might sound unusual in tech but it's pretty normal in other industries. Big banks have federal examiners with desks in the building and every nuclear plant in the US has inspectors who work on site full time. I think frontier AI labs should work the same way and this is a very practical first step.

One non-model thing I'm very excited we announced today with Fable 5.1 is Enterprise Frontier Safeguards (EFS). Even if you're not a CEO/CISO, this blog post is a look into how big companies are thinking about AI adoption which is important to understand if you're interested in how AI might diffuse across industry. Companies are giving agents more and more access to internal systems. With traditional zero data retention, there's been no way to spot patterns in what agents might be doing across sessions on these systems. EFS is ZDR++. It's ZDR built for a world with agents. A company's data stays in its own cloud, and an automated monitoring layer we built flags risky patterns to its team. I think of this as an observability and risk mitigation layer for agents. My guess is it will become a standard requirement from enterprises for running increasingly powerful AI on their systems.

Fable 5.1 is a beast at many things but one thing in particular I have been having a ton of fun with is generating videos through code. For this one I gave it a picture of a property lot. It designed a house for the lot, rendered it, and produced a cinematic walkthrough.

We’ve written an FAQ to answer some of the questions we've received about watermarking. In summary: • We’re implementing watermarking to comply with the EU AI Act. Other major model developers have signed the same Code of Practice and will also be implementing watermarking; • Our watermarking method doesn’t have any practical impact on the quality or content of Claude’s outputs; • The difference between watermarked and un-watermarked text will not be distinguishable to readers; • Nothing is added to the text and there are no hidden characters; • Watermarking doesn’t require extra tokens, and will not be more expensive; • Watermarks can’t be traced to a specific person, organization, or chat. Read more:

Some of my favorite graphs from Opus 5 launch. We put a ton of work into making this model token efficient across domains while still raising the intelligence bar. It feels very smooth to use and I prefer it over Fable 5 for many coding tasks.

Introducing Claude Sonnet 5, our most agentic Sonnet yet. It makes plans, uses tools like browsers and terminals, and runs autonomously at a level that just a few months ago required larger and more expensive models.

This is a new paradigm for interacting with Claude that is significantly more "inline" with all the other human activity org-wide. Once you do all of the under the hood engineering work to make this "just work" (e.g. across tools, integrations, compute environments, memory, security, etc.), Claude basically joins the team in a seamless way - you can talk to it as you would talk to a person and it can help with a very large variety of workloads. Imo this is the 3rd major redesign of LLM UIUX. The first paradigm was that the LLM is a website you go to, the second was that it is an app you download to your computer. This third one is that it is a self-contained, persistent, asynchronous entity with org-wide tools and context, working alongside teams of humans. It really takes a while to wrap your head around it, but it works and it is awesome.

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:

Claude Fable 5 scores very well on FrontierMath: Tiers 1–4 (v2), reaching 87% on Tiers 1–3 and 88% on Tier 4. This continues a streak of Anthropic models improving rapidly at math.