Research @AnthropicAI. Opinions are my own!
San Francisco
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Sonnet 5.5 has the same feel I liked about Opus 5.5. It writes clearly, it's very fast, and it's a major capabilities jump over Sonnet 5. Really great model to iterate with.
Introducing Claude Sonnet 5.5, the second model in the Claude 5.5 family.
It’s a clear upgrade over Sonnet 5, runs more than 30% faster, and costs up to 30% less for most work.
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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
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Prompt in Claude Tag
"Recreate Market Street, San Francisco as it stood on April 17, 1906, the afternoon before the earthquake, in Blender.
Scope: the Ferry Building up Market to Fifth Street, including the Palace Hotel, the Call Building, the Chronicle Building, Lotta's Fountain and the Emporium.
Before modeling anything, build a source file from: the 1899-1905 Sanborn fire insurance maps (footprints, heights, materials, occupants), the Miles Brothers film "A Trip Down Market Street" (April 1906), period photographs from OpenSFHistory, the Library of Congress and the David Rumsey collection, and USGS topography. Record every building with footprint, height, facade material, occupant, and the source for each fact with a confidence level.
Build everything in Blender Python. No downloaded meshes, textures or HDRIs. Write reusable generators (Victorian commercial facade, mansard roof, bay windows, awnings, painted signage, gas and electric street lamps, cable car, horse-drawn wagon, early automobile) and assemble the street from the source file, so every building traces back to data.
Provide a 10 second video up the street."
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I just realized Opus 5.5 can use Blender to make claymations with just a single prompt in claude dot ai now
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need to make sure you've been updated to this (rolling out to everyone soon if you haven't!)
Claude Cowork and chat are merging into one Claude.
Ask a quick question or hand over a report, and Claude takes it from there, even after you close your laptop. If something's unclear, Claude asks—you keep the final say.
Rolling out to Pro and Max over the next few weeks.
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Using Opus 5.5 feels like hitting every green light on your drive home, drinking a cold glass of water when you're thirsty, and a hot shower after a long day.
It's super smart, it writes clearly, it's fast, and it costs way less. It's a very good model.
Introducing Claude Opus 5.5, the first model in our new Claude 5.5 family.
It performs at the level of Claude Fable 5.1 for most tasks, and costs 40% less to run than Opus 5.
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The team did an amazing job with this merge. The resulting UX feels so much better than chat or Cowork did on their own.
And the new slides/docs/design integrations work very well.
Claude Cowork and chat are merging into one Claude.
Ask a quick question or hand over a report, and Claude takes it from there, even after you close your laptop. If something's unclear, Claude asks—you keep the final say.
Rolling out to Pro and Max over the next few weeks.
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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.
We Must Pace the Frontier: I’ve written a new essay on why the AI industry should slow down, with a three-part plan for doing so.
Anthropic is unilaterally committing to the first of these steps. We’ll provide third-party evaluators with permanent, employee-level access to our systems, so that they can verify adherence to our safety measures, report on incidents, and assess models’ alignment during training.
You can read the full post here: darioamodei.com/post/we-must…
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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.
We’re also introducing Enterprise Frontier Safeguards (EFS), which give enterprise customers complete privacy (the same as zero data retention), while still being state-of-the-art at preventing adversarial use. EFS rolls out in phases, starting this fall. anthropic.com/news/enterpris…
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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.
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Alex Albert retweeted
With Fable 5.1 out today, we've also reset 5-hour and weekly limits for all users.
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The way I keep describing Fable 5.1 to people is that it just works.
I explain what I want in a few vague, messy sentences, and it figures out the rest. It fills in the gaps the way I would have. It's a truly impressive model in so many ways and I hope you enjoy using it!
We’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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Alex Albert retweeted
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: anthropic.com/news/claude-te…
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Just over 6 months later, Opus 5 now produces near-superhuman level spreadsheets and slide decks that match what a consultant would make. Things are changing fast.
I'm hearing from many folks across finance industry that Claude for Excel is blowing their minds.
The agentic coding takeoff but for other fields is coming in 2026.
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