OpenAI Codex

Last updated Aug 5, 2026 is a coding agent you run in your terminal. It supports custom model providers ↗︎ defined in config.toml. This configuration adds a provider that points at AI Gateway's OpenAI endpoint, so Codex sends its requests through AI Gateway. AI Gateway authenticates the model provider for you through Unified Billing, so you pass a Cloudflare API token instead of an OpenAI API key. If your gateway is protected by Cloudflare Access, refer to Use with Cloudflare Access.

Note

Codex custom providers only support the OpenAI Responses API (wire_api = "responses"). This means you can only use OpenAI models that support the Responses API, such as gpt-5.5. Models from other providers (for example, Anthropic or Google) do not use the OpenAI Responses request format, so they do not work with Codex through this configuration.

Prerequisites

Before you start, you need:

  • Your Cloudflare account ID. To find it, refer to Find your account and zone IDs.
  • An AI Gateway. You can use your account's default gateway or create a gateway and use its slug.
  • A Cloudflare API token with AI Gateway permission.
  • Credits loaded on your account for third-party models.

  • Codex ↗︎ installed and updated to the latest version.

  • Create a Codex profile ↗︎ file at ~/.codex/cloudflare-aig.config.toml. The profile defines a custom model provider that points at your gateway's OpenAI endpoint and reads your Cloudflare API token from an environment variable.

Replace <ACCOUNT_ID> and <GATEWAY_ID> with your values. You can use default for the gateway to route through your account's default gateway, or change it to another gateway slug.

\~/.codex/cloudflare-aig.config.tomltoml

```toml model_provider = "cloudflare-ai-gateway" model = "gpt-5.5" model_reasoning_effort = "medium"

[model_providers.cloudflare-ai-gateway] name = "Cloudflare AI Gateway" # Run wrangler whoami to get your account ID, then replace . # Use default for to route through your account's default gateway. base_url = "https://gateway.ai.cloudflare.com/v1///openai" env_key = "CLOUDFLARE_API_KEY" wire_api = "responses" ```

Note

Codex does not expand environment variables inside base_url, so the account ID and gateway slug must be literal values. Only CLOUDFLARE_API_KEY is read from the environment. 2. Set your Cloudflare API token as the CLOUDFLARE_API_KEY environment variable. The following commands set it for the current session. To persist it, add it to your shell profile (for example, ~/.zshrc or ~/.bashrc).

Replace <CLOUDFLARE_API_KEY> with your value.

bash # Run `wrangler auth token` to get an auth token. export CLOUDFLARE_API_KEY="<CLOUDFLARE_API_KEY>"

powershell # Run `wrangler auth token` to get an auth token. $env:CLOUDFLARE_API_KEY = "<CLOUDFLARE_API_KEY>"

  1. Start Codex with the profile and send a prompt. Requests now route through AI Gateway. The cloudflare-aig profile name matches the cloudflare-aig.config.toml file you created.

bash codex --profile cloudflare-aig

Use with Cloudflare Access

If your gateway is protected by Cloudflare Access, Codex can authenticate with a short-lived Access token instead of a Cloudflare API token. Point the provider at your custom domain, and configure the provider's auth command to fetch the token with cloudflared instead of passing a token through an environment variable.

Update the same ~/.codex/cloudflare-aig.config.toml profile from the Unified Billing setup so the provider points at your custom domain and uses cloudflared for authentication. The cloudflare-aig in codex --profile cloudflare-aig refers to this file's name. Replace ai-gateway.example.com with your custom domain.

\~/.codex/cloudflare-aig.config.tomltoml

model_provider = "cloudflare-ai-gateway"
model = "gpt-5.5"
model_reasoning_effort = "medium"

[model_providers.cloudflare-ai-gateway]
name = "Cloudflare AI Gateway"
base_url = "https://ai-gateway.example.com/openai"
wire_api = "responses"

[model_providers.cloudflare-ai-gateway.auth]
command = "cloudflared"
args = ["access", "login", "--no-verbose", "https://ai-gateway.example.com"]
timeout_ms = 30000
refresh_interval_ms = 0

Compared to the Unified Billing setup in the previous section, the custom domain replaces the account ID and gateway ID in base_url, and the auth block replaces env_key.

Start Codex with the profile:

codex --profile cloudflare-aig

The first request opens your identity provider's login flow. After you authenticate, requests route through AI Gateway with your Access identity attached as cf.user_id.

To confirm traffic reaches AI Gateway, refer to Verify it works.

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