Act on this, mostly signal

Opus 5.5 Fast mode is out of research preview

What to do

Enable it with speed: fast in the API or /fast in Claude Code for up to 2.5x output speed at a higher price.

Why

It left research preview on October 15 and needs no application or beta header.

What the research found

Opus 5.5 Fast mode left research preview on Oct 15 2026; no application or beta header needed, enabled via speed: fast in API or /fast in Claude Code, up to 2.5x output speed at higher price.

Claims and how well the evidence supports them

Opus 5.5 Fast mode ended its research preview on October 15, 2026 99%
Fast mode no longer requires an access application or the fast-mode-2026-02-01 beta header 98%
Fast mode gives up to 2.5x output tokens per second at a higher token price 99%
Fast mode is enabled with speed: fast in the API or /fast in Claude Code 99%

Evidence

note.com https://note.com/ai__on/n/nf8533b8a4521?hl=en

Actionability rated high.