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Use GPT-5.5 in Codex CLI 0.124.0

Codex hasn't added GPT-5.5 to its built-in model list yet. This guide walks through enabling it manually in 4 steps using model-catalog.json.

#GPT-5.5 #Codex CLI 0.124.0 #model-catalog.json #QCode

Why this guide exists

Codex CLI 0.124.0 only ships GPT-5 / GPT-5-Codex in its default model table. Running /model won't show gpt-5.5, and putting model = "gpt-5.5" directly in config.toml will error out. The official way to extend the registry is model-catalog.json.

Prerequisites

  • A QCode account (required to download the config file)
  • Codex CLI 0.124.0 or later installed
  • QCode already wired into ~/.codex/config.toml

1. Download model-catalog.json

The model registration file for GPT-5.5 is packaged as a zip (~37 KB, ~231 KB after extracting). Click the button below, sign in to QCode, and download it locally.

Sign in to download

The file is only exposed to authenticated QCode users to prevent third-party hotlinking. Any QCode account (free or paid) can download it.

2. Place it in ~/.codex/

Extract the zip to get model-catalog.gpt-5.5.json, then drop it into Codex CLI's config root — the same folder as config.toml and auth.json.

Terminal
# unzip and move
unzip model-catalog-gpt-5-5.zip
mv model-catalog.gpt-5.5.json ~/.codex/

# resulting layout:
#   ~/.codex/
#   ├── auth.json
#   ├── config.toml
#   └── model-catalog.gpt-5.5.json
~/.codex directory listing
Resulting ~/.codex/ directory layout

3. Edit ~/.codex/config.toml

Add one line, model_catalog_json, at the top of config.toml pointing at the file you just placed. Windows users: use double backslashes in the path.

~/.codex/config.toml
# ~/.codex/config.toml
model_catalog_json = "./model-catalog.gpt-5.5.json"

# Windows:
# model_catalog_json = '.\\model-catalog.gpt-5.5.json'

model = "gpt-5.5"
# ... keep the rest of your provider / auth config unchanged

4. Restart Codex CLI and verify

Quit the current session and relaunch codex. Run /model inside — gpt-5.5 should now appear in the list and be the selected model.

Verification output
$ codex
> /model
  ● gpt-5.5          ← enabled
    gpt-5-codex
    gpt-5

FAQ

When will Codex ship GPT-5.5 out of the box?

Expected in Codex CLI 0.125+. Once it ships, you can simply delete the model_catalog_json line. Until then, model-catalog.json is the officially supported extension mechanism.

Is GPT-5.5 priced differently from GPT-5.4?

Live pricing is shown on QCode's /models page (sourced from LiteLLM). Once enabled, your first request is billed automatically at the gpt-5.5 tier — no extra setup needed.

Why does the download require sign-in?

The config file is restricted to authenticated QCode users so it won't get indexed or hotlinked. Free accounts can download it too, and it doesn't consume quota.

gpt-5.5 still not showing up in /model?

First check codex --version is >= 0.124.0, then verify the model_catalog_json path in config.toml and that the JSON file is fully extracted (partial unzip is the most common cause).

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