Turn on fast mode for a tab

Agents: claude, codex · On: phone, desktop

Fast mode asks the model for faster output, at a higher cost in usage. It is a switch per tab, under the effort slider, on the models that have it.

Why you would use it

You are waiting on the agent for something you need now: a fix during an incident, a quick back and forth. Fast mode trades usage for speed on that one tab and leaves your other tabs as they are.

How to use it

1. Tap the model button (#modelpick) in the row under the composer. The slash panel opens on Models.

2. On a model that has fast mode, a row reading Fast, after a lightning bolt, sits under the Effort slider, with the model's note under the title. Tap it (#fast-switch) to turn fast mode on. Tap it again to turn it off.

   

Or type /fast and send it to switch fast mode, /fast on to turn it on, or /fast off to turn it off. The command is never sent to the agent.

What you see

• With fast mode on, the model button shows a lightning bolt after Opus 5.5, and its tooltip ends in . Fast mode on.

• /fast answers with a toast: Fast mode on or Fast mode off. On a model without fast mode it answers Sonnet has no fast mode, with the model's name, and changes nothing. Any other word answers /fast takes on or off.

• If Claude turns fast mode down, the bolt on the model button goes grey and the Fast row says why in amber:

  

  What Claude reports	The amber line
  Usage credits are off on the account	Off: usage credits are not turned on for this Claude account
  The organization does not allow the model	Off: your organization does not allow this model
  Too many fast requests for now	A line saying fast mode is cooling down and comes back on by itself
  Anything else	Off: and Claude's own reason code

• A starred favourite saves fast mode with the model and effort. It shows a bolt beside its effort bars, and picking it turns fast mode on or off to match.

Options and settings

The note under the title comes from the agent: Codex's own words for its fast tier (for example 2x speed, increased usage), and for Claude Faster Opus output, uses usage credits.

Limits and known gaps

• Only Claude and Codex have fast mode, and only on the models their CLIs list with it: Opus on Claude, the models with a Fast tier on Codex.
• Fast mode stays on when you switch the tab to a model without it, and does nothing there. Back on a model that has it, it applies again.
• New tabs start with fast mode off. There is no default in settings. A Codex tab where you never touch the switch runs at the speed your Codex config picks; once you switch it, the tab's setting wins.
• On Claude the amber line appears after the next reply: Claude says how fast mode went at the end of each turn. Close and open the panel to see it.
• Only Claude says why fast mode is off. Codex takes the request with each message and reports nothing back.

Related

• switch-the-model: the button that opens the panel, and which models have fast mode
• set-the-effort: the slider above the Fast row
• slash-menu: favourites that save fast mode with the model