Claude 4 Sonnet is a leaner model, with improvements built on Anthropic's Claude 3.7 Sonnet model. The 3.7 model often had problems with overeagerness and sometimes did more than the person asked it to do, Amodei said. While it's a less resource-intensive model, it still performs well, he said.

Free, Pro, Max, Team, and Enterprise Claude plans can access Claude Sonnet 4 and Opus 4 now, with an extended thinking mode in beta.

Anthropic says Claude Opus 4 is its most powerful model and the best coding model in the world, while Sonnet 4 is replacing Sonnet 3.7 in the chatbot.