Claude Opus 4.8 fast mode is deprecated, gone on 30 November
Anthropic is retiring the speed: "fast" option on Opus 4.8 a month after flagging it. Opus 5.5 keeps the feature, and its fast mode is both quicker and cheaper.
Anthropic deprecated fast mode for Claude Opus 4.8 on 30 October, with removal set for 30 November 2026. After that date, any request to claude-opus-4-8 with speed: "fast" returns an error instead of a faster response.
Fast mode delivers up to 2.5x higher output tokens per second at premium pricing, and on Opus 4.8 it never left research preview. Anthropic’s migration path is Claude Opus 5.5, where fast mode is generally available and, unusually for a deprecation, cheaper: $8 per million input tokens and $40 per million output tokens, against $10 and $50 on Opus 4.8. This is the third time this year Anthropic has sunset fast mode on an older Opus model shortly after shipping it properly on a newer one, after the same pattern with Opus 4.6 in May and Opus 4.7 in June.
{ "model": "claude-opus-5-5", "speed": "fast" }Why it matters: if anything in your stack sets speed: "fast" against claude-opus-4-8, it will start erroring out on 30 November unless you move the model string to claude-opus-5-5 first. Given the lower price, there’s no reason to wait for the deadline.