Mike Krieger

Building at Anthropic Labs @anthropicai.
Before: CPO at Anthropic, co-founder & CTO of @instagram and @artifact_news

[Mike Krieger @mikeyk]

And...Haiku 5.5 will round out the family in the coming weeks.

[Mike Krieger @mikeyk]

Sonnet 5.5, the second release in the 5.5 family, is out! It’s 30%+ faster than Sonnet 5 and up to 30% cheaper for most work.

[Claude @claudeai]

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.

[Mike Krieger @mikeyk]

I still reach for Opus 5.5 for most work, but Sonnet 5.5 is a great complement. I love its design skills and it's great for building features — I use it to make Artifacts often now. Try it out and let us know what you think!

[Mike Krieger @mikeyk]

We’re also launching Claude Sonnet 5.5 and Haiku 5.5 in the coming weeks. These models will come with many of the same improvements to performance, efficiency, and safety.

With that, happy building everyone.

[Mike Krieger @mikeyk]

Go try out Opus 5.5, which we launched today! It leads in coding and knowledge work, and it’s a great writer. It performs at the level of Claude Fable 5.1 for most tasks, and costs 40% less to run than Opus 5.

[Claude @claudeai]

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.

[Mike Krieger @mikeyk]

We’ve always taken safety seriously, and Opus 5.5 underwent extensive alignment testing, evaluation by outside organizations like METR. It also introduces safeguards across high-risk areas like cyber and bio.

[Mike Krieger @mikeyk]

Omid and the team did great work on this one. Most of my Claude Desktop work these days is in these new-style projects and I've really enjoyed how easy it is to kick off a bunch of work while still having a coordinator Claude responding quickly

[Omid Mogasemi @OmidMogasemi]

Super excited to show the world Projects!!

We've been building this for the last few months and it has become my new daily driver. A few tips for getting the most out of it 🧵

[Mike Krieger @mikeyk]

I had trouble picturing the whole Iron Tangle level from Dungeon Crawler Carl, so I made an interactive artifact and I think I finally understand it: https://t.co/sdiCBDbHQV

[Mike Krieger @mikeyk]

Also new today: Claude Docs, Claude Slides and Claude Design are now available in every conversation, powered by a revamped Artifacts platform.

Ask for a design, deck, or document. Get back something you can edit, download, and take anywhere.

Try it out for yourself and let us know what you think.

[Mike Krieger @mikeyk]

Claude Cowork and Chat are now one Claude, starting today.

The most common thing we hear: people aren't sure which product to start with. That friction gets in the way of getting the best from what these models can do.

I've been on the unified version for a few weeks and really enjoy it. Claude does the deciding about how to get there, while I get to keep my thinking on the work itself.

Let us know what you think! We'll be getting it dialed in over the coming weeks.

[Claude @claudeai]

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.

[Mike Krieger @mikeyk]

Channeling my cogsci background, I asked it to build an interactive model of the human brain tracing what happens when you hear "could you pass the salt?" It reasoned through the anatomy on its own using no external assets. You can try it here: https://t.co/2MPyM31ykF

[Mike Krieger @mikeyk]

We launched Claude Fable 5.1 this morning! Fable models are built for complex, multi-step work that runs on its own, and Fable 5.1 sets a new standard across coding, knowledge work, and long-running problem-solving tasks.

[Claude @claudeai]

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.

[Mike Krieger @mikeyk]

It's also more honest as it works. Give it a target and it works until it gets there, and when it's stuck it says so instead of reporting success. It’s the same price as Fable 5 ($10/$50), and we've cut the price of cache reads 75% to $0.25/MTok on the API.

[Mike Krieger @mikeyk]

Also notably — for both those games, the prompt was ~4 sentences and used dynamic /workflows extensively. Compared to earlier in the year where I had a bespoke harness/verification system, the models can do so much more with so much less instruction.

[Mike Krieger @mikeyk]

Opus 5 quickly became my daily driver both at work and on the weekends. It can work for hours on complex tasks, and I've found it consistently gets to the bottom of tricky tasks. I also had some fun building some games with it 🧵

[Claude @claudeai]

Introducing Claude Opus 5.

It's a thoughtful and proactive model that comes close to the frontier intelligence of Fable 5 at half the price.

[Mike Krieger @mikeyk]

I also had Opus 5 help me realize an idea I had when I was 6 years old — I loved Transport Tycoon and I wanted the ability to walk around in that world. Opus worked overnight to create a renderer, savegame parser, and boat/plane/truck/bus simulator:

https://t.co/GmWruauaLa

[Mike Krieger @mikeyk]

@android_stern I use Fable a bunch too, but it's also really important to use upcoming models thoroughly before release

[Mike Krieger @mikeyk]

New today as Claude Cowork starts rolling out to web and mobile: Chat and Cowork now share one home tab on web and desktop — one sidebar, one search, and one place for your Projects & Artifacts. Keep an eye out for even better Chat + Cowork integration soon, too.