Per-message effort changes enter beta on the Claude API
Tech · Releases · Tue, September 1, 2026
A role system message carrying output_config.effort inside messages changes effort for later turns while preserving the prompt cache, on Claude Fable 5.1, Mythos 5.1 and Opus 5. Requests need the mid-conversation-output-config-2026-07-01 be
Every year
Also on Sep 1, 2026
| Date | Event | When |
|---|---|---|
| Tue, Sep 1, 2026 | Bear season opens (MN) | Now |
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- 2026-09-25: added to 2026-09-01