Command reference ยท Codex CLI
/reasoning
No standalone command in the Codex terminal CLI, see /model
According to the general Codex slash commands reference (there explicitly headed as a reference for the ChatGPT desktop app), /reasoning selects the reasoning effort for the current chat.
Important limitation for the terminal CLI: /reasoning does not appear in the CLI's own "Built-in slash commands" table on the reference page for the CLI interface, and no command with this name exists in the Codex CLI's open-source code (file slash_command.rs) either. There, /model takes over this task instead โ according to the source code literally described as "choose what model and reasoning effort to use". The reasoning effort concept is generally real in Codex, though, and is actively being developed further: release notes from July 2026 mention new levels such as "Max" and "Ultra" in addition to the familiar ones. In the terminal CLI, you set the reasoning depth via /model, not via a standalone /reasoning command.
โ WHEN TO USE IT?
Adjust reasoning depth in the desktop composer
Call /reasoning to choose between more thoroughness and more speed for the current chat in the ChatGPT desktop app composer โ documented there as a separate command.
Same goal in the terminal CLI
In the Codex terminal CLI, call /model instead, which according to the source code sets both model and reasoning effort together.
โ WHEN NOT TO?
Expecting the command in the terminal CLI
/reasoning is missing both from the CLI reference table and from the Codex CLI's open-source code (no SlashCommand::Reasoning).
Better: use /model in the terminal CLI
Only switching the model
Where available, /reasoning only changes the reasoning effort, not the model itself.
Better: use /model to also switch the model
SOURCES
- Codex CLI docs: Slash Commands โ learn.chatgpt.com
MORE COMMANDS ยท Codex CLI