How to Enable Codex in Cursor

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In Cursor, you can use it as a native model for Chat and Composer or through the dedicated Codex Extension for more advanced "Reasoning Effort" control.

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1. Open the Cursor application on your computer.
2. Click File on the toolbar and locate Preferences.
3. Choose Cursor Settings from the dropdown menu.
4. Click on the Models tab in the sidebar of the settings window.
5. Find GPT-5.3 Codex in the list and toggle it On.
6. Close the settings tab to save your changes.
7. To use the model for your current task, open the Chat (Ctrl + L) or Composer (Ctrl + I).‍
8. Select GPT-5.3 Codex from the model dropdown at the bottom.