Claude Opus 5.5 fast mode leaves research preview: no access request, no beta header, and a default rate limit in every usage tier
Fast mode for Opus 5.5 moves from request-only to available by default, so turning it on is now a parameter change.
// Key points
- Fast mode for Claude Opus 5.5 no longer needs an access request, and requests no longer need the fast-mode-2026-02-01 beta header; requests that still send it keep working.
- Claude Opus 5.5 now has a default fast mode rate limit in every usage tier.
- Fast mode for Claude Opus 5 and Claude Opus 4.8 stays in research preview and still needs the beta header.
- The same day, Opus 5.5 fast mode became available on Claude in Microsoft Foundry for deployments hosted on Azure.
Builder's takeFast mode used to require an application, so I only tried it in demos; now that it’s on by default, it can go into production paths. I’d turn it on only where a user is waiting live, such as follow-up question generation in AI Interview, and keep batch jobs on the standard tier; the release note doesn’t mention price, so check billing in the Console first. Read alongside the 10-11 GPT-6.1 Sol Ultrafast item, charging by speed tier is becoming standard across vendors.
// Background · from #Anthropic
Full timeline →- Oct 16 Anthropic gives METR employee-like access to its systems, onboarding six METR staff with company hardware, and lets it publish its findings
- Oct 15 Claude API launches OpenTelemetry export in beta to trace Messages API requests and Managed Agents sessions
- Oct 15 Claude Code 2.1.299 compacts 200K+ token conversations after about 54 idle minutes, before the one-hour prompt cache expires