Claude Opus 5.5 fast mode leaves research preview: no access request, no beta header, default rate limits by tier
Synopsis
Anthropic's Claude Platform release notes say fast mode is out of research preview for Claude Opus 5.5: developers no longer request access, requests no longer need the fast-mode-2026-02-01 beta header, and requests that still send it keep working. Claude Opus 5.5 now carries a default fast mode rate limit in the Start, Build, and Scale usage tiers, and fast mode reaches Claude in Microsoft Foundry deployments hosted on Azure. Fast mode for Claude Opus 5 and Claude Opus 4.8 remains in research preview and still requires the beta header.
Interpretation
Fast mode for Claude Opus 5.5 moves from research preview to general availability, so callers no longer request access separately. Fast mode had been a research preview that required requesting access; that step is removed for Opus 5.5. The release notes list the change under October 15, 2026 and state that requests no longer require the fast-mode-2026-02-01 beta header.
Migration cost is kept low: existing requests that still send the beta header are not rejected. Enabling a preview feature usually meant editing request headers; the old form keeps working here. The release notes state that requests that still send the fast-mode-2026-02-01 header keep working.
Fast mode on Opus 5.5 now has a default rate limit, organized by the Start, Build, and Scale usage tiers. As a research preview, fast mode's rate limits and access were handled separately. The release notes say Claude Opus 5.5 now has a default fast mode rate limit in the Start, Build, and Scale usage tiers.
Fast mode reaches Claude in Microsoft Foundry deployments hosted on Azure with Opus 5.5. That deployment path was not previously listed among fast mode's availability. The release notes list Foundry availability as a third change published the same day.
Perspective
The change covers Claude Opus 5.5: on the Claude API it no longer requires requesting access or the fast-mode-2026-02-01 beta header, and a default fast mode rate limit applies in the Start, Build, and Scale usage tiers; the same day also opened fast mode for Claude in Microsoft Foundry deployments hosted on Azure. Fast mode for Claude Opus 5 and Claude Opus 4.8 remains in research preview, and fast mode requests to those models still need the beta header.
The release notes give no speed multiplier for fast mode relative to standard speed and no numeric fast mode rate limits for each usage tier. Fast mode for Opus 5 and Opus 4.8 is still labeled research preview, and the notes do not say when those will graduate.