Claude Opus 5.5 launches with a 1M token context window and 128k output

GASep 22, 2026VerifiedAdded Sep 22, 2026

Anthropic released Claude Opus 5.5 for long-running agentic coding and knowledge work, with a default 1M token context, 128k max output and always-on adaptive thinking. It costs $4 / $20 per MTok, below Claude Opus 5, and is on the Claude API, Bedrock, Google Cloud and Microsoft Foundry.

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Read Anthropic's release notes

https://platform.claude.com/docs/en/release-notes/overview#september-22-2026

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