Fast Mode System Prompt Context / Claude Code v2.1.36

The system prompt now includes <fast_mode_info> context explaining fast mode to Claude: > "Fast mode for Claude Code uses the same Claude Opus 4.6 model with faster output. It does NOT switch to a different model. It can be toggled with /fast."

Evidence

System prompt template (search for "<fast_mode_info>")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.36 →

The build it came inv2.1.36

7 Feb 2026 · 5 entries, this one is #4.

Either side of it

v2.1.34Older
v2.1.37Newer

Open the release →

Names in this entry

slash/fast
Toggle fast mode on or off. Run it while Claude is responding and Claude Code toggles fast mode without waiting for the turn to end, though the running turn finishes at its original speed. Before v2.1.242, Claude Code decided from a feature flag it fetched from Anthropic whether to run the command mid-turn or queue it until the turn finished, and always queued it in a session that doesn't fetch feature flags. Availability in non-interactive mode with -p is limited; see Toggle fast mode. Requires Claude Code v2.1.205 or later

Is this right?

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.