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Codex Desktop API Key Setup — config.toml & auth.json Guide

How to configure Codex Desktop with a custom API key and OpenAI-compatible base URL from APIMaster.ai. Same ~/.codex setup as Codex CLI. Works for official subscription users who want discounted GPT-5.4 access.

Codex Desktop is OpenAI’s desktop coding agent. You can point it at APIMaster.ai with the same local config files as Codex CLI: ~/.codex/config.toml and ~/.codex/auth.json.

One setup covers Codex Desktop and Codex CLI. After you finish this guide, Desktop should show Logged in with API key and provider apimaster.

Prerequisites: Environment check, API key.

APIMaster.ai

Item Value
Base URL https://apimaster.ai/v1
API Key Console
Models Marketplace or GET /v1/models

Codex uses https://apimaster.ai/v1 (OpenAI-compatible). No pricing or model guarantees in this doc.

Configure Codex (Desktop + CLI)

Codex home: ~/.codex/ (macOS) or %USERPROFILE%\.codex\ (Windows). Quit Codex Desktop before editing files.

Back up, then replace (required)

If config.toml or auth.json already exist (official Codex login or another API provider):

  1. Copy backups, e.g. config.toml.bak and auth.json.bak, in the same folder.
  2. Overwrite each file completely with the snippets below — do not add APIMaster lines to the bottom of your old config or keep duplicate [model_providers.*] sections.

To restore later, rename your .bak files back to the original names.

Windows

Win + R → %userprofile%\.codex — create the folder if missing. Then replace config.toml and auth.json entirely:

config.toml

disable_response_storage = true
model = "gpt-5.4"
model_provider = "apimaster"
model_reasoning_effort = "high"
model_verbosity = "high"

[features]
web_search_request = true

[model_providers.apimaster]
base_url = "https://apimaster.ai/v1"
name = "apimaster"
requires_openai_auth = true
wire_api = "responses"

auth.json

{
  "OPENAI_API_KEY": "YOUR_API_KEY"
}

Replace YOUR_API_KEY with your APIMaster key from the Console.

macOS

Open ~/.codex (Finder: Go → Go to Folder… → ~/.codex). Back up any existing files, then replace config.toml entirely:

config.toml

model_provider = "apimaster"
model = "gpt-5.4"
model_reasoning_effort = "high"
network_access = "enabled"
disable_response_storage = true
model_verbosity = "high"

[model_providers.apimaster]
name = "apimaster"
base_url = "https://apimaster.ai/v1"
wire_api = "responses"
requires_openai_auth = true

auth.json — same as Windows.

Notes

  • Set model to gpt-5.5 etc. per Supported models.
  • If wire_api = "responses" fails on your Codex version, try wire_api = "chat" or remove the line.
Issue Fix
401 Check auth.json key
404 Model id + account access
Timeout base_url must be exactly https://apimaster.ai/v1

Verify Codex Desktop

  1. Reopen Codex Desktop.
  2. Confirm Logged in with API key and provider apimaster in the UI.
  3. Start a chat — you should get replies through APIMaster.

CLI users can also run codex in a terminal to verify the same config.

Advanced: switch official subscription ↔ APIMaster

Use this only if you already use the official ChatGPT subscription in Codex Desktop and want to keep project sidebar history when you hit the rolling 5-hour usage limit.

Manually editing config.toml in that situation often hides project threads. codex-provider-switcher switches provider mode and syncs conversation metadata locally — no upload, no deletion of chat content.

When to use this

  • Official subscription shows You're out of Codex messages or Usage remaining near 0% with Resets every 5 hours.
  • You want to continue in the same project threads on APIMaster, then switch back to official when the limit resets.

Rate limit banner

What the tool does

Repo: github.com/RomaCredit/codex-provider-switcher

  • Updates local Codex config (config.toml, auth.json, SQLite, session metadata)
  • Saves APIMaster and official profiles
  • Backs up before changes under ~/.codex/provider-switcher

Windows

  1. Quit Codex Desktop completely.
  2. Double-click codex-provider-menu.bat.
  3. Choose 1 (APIMaster) or 2 (official). Enter API key on first APIMaster switch.
  4. Reopen Codex Desktop — expect Logged in with API key, apimaster provider, and your project threads still visible.

APIMaster mode with history synced

Menu

If sidebar history is wrong: option 6. Repair Desktop history list.

PowerShell:

.\switch-codex-provider.ps1 status
.\switch-codex-provider.ps1 apimaster
.\switch-codex-provider.ps1 official
.\switch-codex-provider.ps1 repair-history

macOS

chmod +x ./codex-provider-menu.command
./codex-provider-menu.command

Or:

python3 codex_provider_switcher.py apimaster
python3 codex_provider_switcher.py official
python3 codex_provider_switcher.py repair-history

Security

  • Keys and backups stay on your machine only.
  • Do not paste .codex folders into public issues.
  • Quit Codex Desktop before switching.

FAQ (switcher)

Question Answer
History preserved? Session files remain; tool syncs metadata for sidebar display.
Switch back to official? Yes — menu 2 or official.
Key location? Local ~/.codex/auth.json and tool profiles.
Deletes chats? No.

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