api update

What's new in Claude Opus 5

2 months ago

Claude Opus 5 is a significant improvement over Opus 4.8, with gains in deep reasoning, agentic tasks, long-horizon tasks, and test-time compute scaling.
Thinking is enabled by default on Claude Opus 5; disabling thinking is restricted to effort levels high or below, and attempting to disable it with xhigh or max effort returns a 400 error.
The model supports a 1M token context window, 128k max output tokens, and an effort ladder from low to max for controlling reasoning depth.
Mid-conversation tool changes are in beta, allowing tools to be added or removed between turns while preserving the prompt cache.
A new 'default' mode for fallbacks applies Anthropic's recommended fallback models by refusal category, requiring a beta header.
The minimum cacheable prompt length is reduced from 1,024 to 512 tokens, enabling caching for shorter prompts without code changes.
Fast mode is in research preview for Claude Opus 5 on the API only, priced at $10 per million input tokens and $50 per million output tokens.
In agentic sessions, the model narrates progress more often, delegates to subagents more readily, and verifies its own work, so verification instructions from earlier models cause over-verification.
Claude Opus 5 delivers frontier intelligence at half the cost of Claude Fable 5, with pricing unchanged from Opus 4.8 at $5 per million input tokens and $25 per million output tokens.
The model is available on Anthropic API, Amazon Bedrock, Google Cloud Vertex AI, and Microsoft Foundry; migration requires updating the model ID and reviewing behavior changes.

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What's new in Claude Opus 5