We’ve deprecated fast mode for Claude Opus 4.8, with removal on November 30, 2026

Anthropic has deprecated fast mode for Claude Opus 4.8 and will remove it on November 30, 2026. After removal, requests to claude-opus-4-8 with speed: "fast" will return an error.

To keep using fast mode, migrate to Claude Opus 5.5, which accepts speed: "fast" without a beta header. Check your other settings when moving: Opus 5.5 enables thinking when the thinking field is omitted and doesn't support Priority Tier.