Codex custom API provider setup

---
title: Codex custom API provider setup
description: Configure a Relyven custom provider for Codex with the OpenAI-compatible Responses API.
lastUpdated: 2026-07-29
---

This page configures Codex directly. To switch Codex and Claude providers from one desktop app, use the [CC Switch guide](/en/integrations/cc-switch/).

## Before you start

- Install Codex and confirm the `codex` command runs.
- Create a Relyven key that can use the model you need.
- Copy the exact model ID from the dashboard.

## Add the Relyven provider

Edit the user-level `~/.codex/config.toml`, not a project `.codex/config.toml`:

```toml
model = "YOUR_MODEL_ID"
model_provider = "relyven"

[model_providers.relyven]
name = "Relyven"
base_url = "https://api.relyven.com/v1"
env_key = "RELYVEN_API_KEY"
wire_api = "responses"
```

Put the key in an environment variable:

```bash
export RELYVEN_API_KEY="YOUR_API_KEY"
codex
```

The Base URL must include `/v1`. Codex appends `/responses`, so do not enter the complete endpoint in `base_url`.

## Verify the provider

Check the API before testing the client:

```bash
curl https://api.relyven.com/v1/responses \
  -H "Authorization: Bearer $RELYVEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"YOUR_MODEL_ID","input":"Reply with OK."}'
```

Then start a new Codex task that requires a tool call. Relyven supports `/v1/responses` and the legacy `/responses` compatibility path.

Relyven does not intentionally change `tools`, reasoning fields, service tier, session fields, context, or the requested model. Unsupported combinations may still be rejected by the selected model.

## Troubleshooting

| Result | Check |
|---|---|
| `401` | `RELYVEN_API_KEY` is exported in the shell that starts Codex |
| `403` | The key can use the configured model |
| `400` | `wire_api = "responses"`, model ID, and request fields |
| Model not found | Copy the ID from the authenticated model list or dashboard |
| Configuration did not change | Exit Codex completely and start a new session |

See [Responses API](/en/api/responses/) for request fields and [API error handling](/en/api/errors/) for retry guidance.

This page configures Codex directly. To switch Codex and Claude providers from one desktop app, use the CC Switch guide.

Before you start

Install Codex and confirm the codex command runs.
Create a Relyven key that can use the model you need.
Copy the exact model ID from the dashboard.

Add the Relyven provider

Edit the user-level ~/.codex/config.toml, not a project .codex/config.toml:

model = "YOUR_MODEL_ID"
model_provider = "relyven"

[model_providers.relyven]
name = "Relyven"
base_url = "https://api.relyven.com/v1"
env_key = "RELYVEN_API_KEY"
wire_api = "responses"

Put the key in an environment variable:

export RELYVEN_API_KEY="YOUR_API_KEY"
codex

The Base URL must include /v1. Codex appends /responses, so do not enter the complete endpoint in base_url.

Verify the provider

Check the API before testing the client:

curl https://api.relyven.com/v1/responses \
  -H "Authorization: Bearer $RELYVEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"YOUR_MODEL_ID","input":"Reply with OK."}'

Then start a new Codex task that requires a tool call. Relyven supports /v1/responses and the legacy /responses compatibility path.

Relyven does not intentionally change tools, reasoning fields, service tier, session fields, context, or the requested model. Unsupported combinations may still be rejected by the selected model.

Troubleshooting

Result	Check
`401`	`RELYVEN_API_KEY` is exported in the shell that starts Codex
`403`	The key can use the configured model
`400`	`wire_api = "responses"`, model ID, and request fields
Model not found	Copy the ID from the authenticated model list or dashboard
Configuration did not change	Exit Codex completely and start a new session

See Responses API for request fields and API error handling for retry guidance.