Codex reads its settings from ~/.codex/config.toml and several other files, and a key written in the wrong place is quietly ignored. Config Studio for Codex lets you set what you want, shows the exact file before it exists, and hands it over without touching your disk. In this lesson you set your model and take the file away.
Open the studio
Open Config Studio for Codex. It starts on Configure, with three columns: the surfaces Codex reads on the left, the one you are editing in the middle, and the file it would write on the right. Nothing you do here is written to your computer; you take the result away at the end.
Pick a surface
The list on the left is every file and setting Codex reads: config.toml: model and defaults, Sandbox and approvals, Rules (.rules files), AGENTS.md, Hooks, MCP servers, the status line and the rest. The first one, config.toml: model and defaults, is open. Its first control, Which config.toml, chooses between yours (~/.codex/config.toml) and the repository's (.codex/config.toml), which Codex reads only in a project you trust.
Open Where it lives under the description to see every place this surface is read from, highest first.
Set the model
In Model, type a model id or pick one from the list, for example gpt-6.1-sol. The box beside the control is ticked: the surface is now in your plan. Below it, Reasoning effort sets how hard the model thinks; leave it unset to keep Codex's default.
Only what you set is written. A key you never touched stays out of the file, so nothing you did not choose overrides what you already have.
Read the file it writes
The right column now shows ~/.codex/config.toml with your line in it. It shows what the open surface writes. Set something on another surface that also writes config.toml, such as the sandbox, and both go into the same file: a line under the file says how many lines the other surfaces add, and See the whole file opens it. Config Studio for Codex writes it as one valid TOML file, every key before the first [table], so nothing lands in the wrong table.
The grey text in an empty field is an example, not a value. A surface whose fields are all grey writes nothing; Fill in the example on the right puts the example into the empty fields so you can edit it from there.
Take it with you
Open Changes. It lists every key you moved and every file the plan writes. Then:
- Download the files gives you the files, with a note saying where each one goes.
- install.sh gives you one script. It sets your old files aside first, then merges into the
config.tomlyou already have, keeping your trusted projects and every other key, and leaves anundo.shbeside the old files that puts them back. It needs Python 3.11 or later.
Read the script before you run it; that is what it is for.
Next: set Codex's sandbox and approvals, the two settings that decide what Codex may do unattended.