Claude Opus 5 Launched with 1M Token Context and Breaking Change
Anthropic has launched Claude Opus 5, a significant upgrade featuring a 1 million token context window, 128k max output tokens, and 'thinking' enabled by default. This update introduces a breaking change regarding the disabling of the 'thinking' parameter at higher effort levels. The new model is available via API and across major cloud platforms, with pricing unchanged from its predecessor.
- →Claude Opus 5 released with expanded context and output capabilities
- →Breaking change in disabling 'thinking' parameter
- →Mid-conversation tool changes in beta
- →Beta support for default server-side fallbacks
- →Full effort ladder support on Claude Opus 5
Breaking changes (1) ›
- Breaking change in disabling 'thinking' parameter
On Claude Opus 5, disabling the 'thinking' parameter is now restricted to effort levels 'high' or below. Using 'xhigh' or 'max' with 'thinking' disabled will result in a 400 error, a change from Claude Opus 4.8.
Features (3) ›
- Claude Opus 5 released with expanded context and output capabilities
Claude Opus 5 offers a 1 million token context window and 128k maximum output tokens, with 'thinking' enabled by default. Pricing remains the same as Claude Opus 4.8.
- Mid-conversation tool changes in beta
A new beta feature on Claude Opus 5 allows for adding or removing tools during a conversation while preserving the prompt cache. This requires the `mid-conversation-tool-changes-2026-07-01` beta header.
- Beta support for default server-side fallbacks
The `fallbacks` parameter now includes a 'default' mode in beta, which utilizes Anthropic's recommended fallback models based on refusal category. This feature requires the `server-side-fallback-2026-07-01` beta header.
Enhancements (1) ›
- Full effort ladder support on Claude Opus 5
Claude Opus 5 supports the entire effort ladder, including the 'max' level for demanding, capability-critical tasks.
https://platform.claude.com/docs/en/release-notes/overview
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