/fast mode doesn't work

What version of Codex CLI is running?

codex-cli 0.110.0

What subscription do you have?

Pro

Which model were you using?

gpt-5.4

What platform is your computer?

Linux 6.17.0-14-generic x86_64 x86_64

What terminal emulator and version are you using (if applicable)?

_No response_

What issue are you seeing?

Codex CLI version: 0.110.0
OS: Ubuntu
Plan: ChatGPT Pro

Repro:

1. Run codex --model gpt-5.4
2. Session starts and shows model: gpt-5.4 xhigh
3. Type /fast

Actual result:
Unrecognized command '/fast'. Type "/" for a list of supported commands.

What steps can reproduce the bug?

Repro:

1. Run codex --model gpt-5.4
2. Session starts and shows model: gpt-5.4 xhigh
3. Type /fast

What is the expected behavior?

Expected result:
/fast should be available, or the docs should clarify why it is unavailable in this setup.

Additional information

_No response_