Opus migration changedmodels/opus-5/migration-guide
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223223* Audit requests that disable thinking: `thinking: {type: "disabled"}` with effort `xhigh` or `max` returns a 400 error, enforced on each request. Re-enable thinking or lower the effort to `high` or below.
224224* If you removed sampling parameters during the Opus 4.7 migration, no action is needed. If you re-added them with a 400-retry path, remove that retry path.
225225* Re-evaluate your `effort` setting: run a fresh [effort](https://platform.claude.com/docs/en/build-with-claude/effort) sweep on your own evals rather than carrying over a setting tuned for Claude Opus 4.7. Test `low` and `medium` effort as cost and latency controls, and `max` effort where maximum capability matters more than token spend. If you run at `xhigh` or `max` effort, raise `max_tokens` to at least 64k as a starting point.
226* Remove any context-window beta header. The 1M context window is the default on the Claude API, Amazon Bedrock, Google Cloud, and Microsoft Foundry.
226* Remove any context-window beta header. The 1M context window is the default on the Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud, and Microsoft Foundry.
227227* If you rebuild conversation history to update instructions, consider switching to a mid-conversation system message to preserve prompt cache hits.
228228* Verify your stop-reason handling reads `stop_details` on refusals (available since Claude Opus 4.7; now publicly documented), and consider `fallbacks: "default"` (beta) to re-run refused requests on a recommended fallback model automatically.
229229* Review prompts near the caching minimum: prompts of 512 tokens or more can now create cache entries.
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