Command reference ยท Codex CLI
/fast
Turns a Fast service tier on or off, when available.
/fast turns a so-called Fast service tier for the currently selected model on or off, provided the model catalog offers such a tier for that model at all. The Fast tier prioritizes response speed; whether it exists depends on the respective model and catalog, not on any manual configuration on your part. Your choice is remembered for the current session.
Unlike /worktree or /cloud, /fast is documented both in the pure terminal CLI command list and in the general Codex command reference โ so it's a genuine terminal CLI feature, not a desktop-app-exclusive one. Despite the terse name, it's not an easter egg but an officially documented feature for model control, alongside /model (full model selection) and /reasoning (reasoning effort).
โ WHEN TO USE IT?
Prefer faster responses when the current model offers a Fast tier
/fast
Check after switching models whether the Fast setting still makes sense
switch /model, then call /fast again
โ WHEN NOT TO?
The current model doesn't offer a Fast tier
According to the docs, /fast only has an effect if the model catalog provides a Fast tier for the selected model at all.
Better: choose a model with Fast support via /model
SOURCES
- Codex CLI docs: Slash Commands โ learn.chatgpt.com
MORE COMMANDS ยท Codex CLI