
Anthropic deprecated fast mode for Claude Opus 4.8 on 30 October 2026[1]. It will be removed on 30 November, and after that, requests to claude-opus-4-8 with speed: "fast" will return an error[1,2].
To keep using fast mode, Anthropic says to migrate to Claude Opus 5.5[1,2]. The steps are in its guide to migrating from Opus 4.8 to Opus 5.5[2].
Fast mode runs the same model with a faster inference configuration, with no change to intelligence or capabilities[2]. Output tokens per second are up to 2.5 times higher[2].
Per million tokens, fast mode costs $10 input and $50 output on Opus 4.8 and Opus 5, and $8 input and $40 output on Opus 5.5[2]. The price is a multiplier on standard rates across the full context window, including requests over 200k input tokens[2]. Prompt caching and data residency multipliers apply on top[2].
Fast mode on Opus 4.8 and Opus 5 is in research preview and available only on the Claude API[2]. Requests need the fast-mode-2026-02-01 beta header, and access to fast mode on Opus 5 requires contacting an account manager or joining the waitlist[2].
Fast mode on Opus 5.5 needs no beta header and runs on the Claude API, Claude Models on Google Cloud (Anthropic managed) and Microsoft Foundry hosted on Azure[2]. Its rate limit is granted by default in the Start, Build and Scale usage tiers[2].
Fast mode is not available with the Batch API or with a Priority Tier commitment[2]. A request that exceeds the rate limit can be retried at standard speed, but requests at different speeds do not share cached prefixes, so the prompt cache misses[2].