Claude Fable 5.2 launches with a 1M token context window and 128k max output

Claude Fable 5.2 is built for demanding reasoning and long-horizon agentic work. It has a 1M token context window, 128k max output tokens, and always-on adaptive thinking.

Who is affected:

Developers building long-running reasoning and agent workloads can move to the new model.

Suggested next step:

Read the migration guide before switching, since the prefix check and computer use changes apply.