Claude Sonnet 4.5 was released yesterday. Anthropic credibly describes it as the best coding, agentic and computer use model in the world. At least while I learn more, I am defaulting to it as my new primary model for queries short of GPT-5-Pro level.

I’ll cover the system card and alignment concerns first, then cover capabilities and reactions tomorrow once everyone has had another day to play with the new model.

It was great to recently see the collaboration between OpenAI and Anthropic where they evaluated each others’ models. I would love to see this incorporated into model cards going forward, where GPT-5 was included in Anthropic's system cards as a comparison point, and Claude was included in OpenAI's.