fast_mode not active when launching cli by default

What version of Codex CLI is running?

service_tier

What subscription do you have?

pro

Which model were you using?

gpt-5.4

What platform is your computer?

windows

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

powershell

What issue are you seeing?

fast_mode is not on by default contrary to the release notes claim

"Fast mode is now enabled by default, and the TUI header shows whether the session is running in Fast or Standard mode. (https://github.com/openai/codex/pull/13450, https://github.com/openai/codex/pull/13446)"

for it to actually launch in fast mode, it also need service_tier=fast

without that, the cli will not display the "fast" purple message next to the reasoning tier in the model description at the top on launch

codex -c "service_tier=fast" does actually start in fast mode tho as far as i could test

What steps can reproduce the bug?

launch codex on a fresh session without using /fast once inside. then it will start without fast mode enabled.

i noticed that if you close codex while it is in fast mode, launching it back in the same terminal will maintain the fast mode status but you must do the /fast command once (which is a problem for non interactive cli)

as mentioned, the service_tier=fast does address this.

What is the expected behavior?

launching with gpt 5.4 should be in fast mode by default if we go with the release note. (personally i think we should have a dedicated --fast_mode parameter instead.

Additional information

_No response_