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Codex is OpenAI’s open-source coding agent for the terminal (Apache-2.0, source). It works from natural-language instructions to edit code across your project, run commands, and complete tasks end to end. Codex reads its model providers from a config file, so adding Opper as one provider lets you run it on Claude, Gemini, DeepSeek, or any other model in the catalog.

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Setup

One command, no config files:
This writes a [model_providers.opper] block into ~/.codex/config.toml and starts Codex. --model is optional.
To configure it by hand, add the provider to ~/.codex/config.toml:
Then export your key and start Codex:

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Choosing a model

Pass any Opper model ID with --model, or set a default in config.toml:
Codex needs tool calling and streaming — pick a model the catalog marks with the tools capability. Browse IDs in the model catalog.

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Troubleshooting

Check that OPPER_API_KEY is exported in the shell running Codex, and that env_key in config.toml names that same variable. Opper keys start with op-.
Copy the model ID exactly from the catalog — it includes the provider prefix, as in anthropic/claude-sonnet-4-6.
model_provider = "opper" has to sit at the top level of config.toml, not inside the [model_providers.opper] table. TOML tables capture every key that follows them.

Traces

Every Codex call, with model, latency, and tokens.

All integrations

Every app that runs on Opper.