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Claude Opus 5.5 fast mode exits preview, drops its beta header

You no longer need a waitlist or the fast-mode-2026-02-01 header to use fast mode on Opus 5.5. Opus 5 and Opus 4.8 stay in research preview.

Source: Claude Platform release notes

Anthropic moved fast mode for Claude Opus 5.5 out of research preview on 15 October. You no longer need to request access, and requests no longer need to carry the fast-mode-2026-02-01 beta header, though requests that still send it keep working.

Opus 5.5 now has a default fast mode rate limit built into the Start, Build and Scale usage tiers, rather than requiring separate enrolment. Fast mode for Claude Opus 5 and Claude Opus 4.8 remains in research preview, so calls to those two models still need the beta header. The same day, fast mode for Opus 5.5 also landed on Claude in Microsoft Foundry for deployments hosted on Azure.

Fast mode trades a premium price for faster token generation, with the same output as standard requests, just delivered quicker. Moving Opus 5.5 to general availability removes the step of joining a waitlist or getting an account manager to flip it on.

Why it matters: if you’re calling Opus 5.5 for anything latency-sensitive, fast mode is now a config choice rather than a request you have to make first, and it ships with a predictable rate limit instead of an ad hoc allowance.

The caveat: if your code still pins the beta header for Opus 5.5, nothing breaks, but you can drop it. Opus 5 and 4.8 integrations still need to keep it.

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