Codex CLI and uttapen: why it does not work today
Since February 2026 Codex CLI speaks only the Responses API, which uttapen does not serve. Here is the full story and the terminal agents that do work.
Updated: 22 Sep 2026
Current versions of Codex CLI do not work with uttapen. The tool speaks only the Responses API, and uttapen doesn't serve that path, so every call returns 404. There is no workaround in the current release.
What happened
Codex CLI used to let you define a custom provider in ~/.codex/config.toml with wire_api = "chat", which worked against any Chat Completions endpoint. That option was deprecated in December 2025 and removed outright in version 0.95.0 (February 2026). Since then wire_api = "responses" is the only accepted value, and the binary itself errors out if it sees chat.
uttapen serves /v1/chat/completions, /v1/completions, /v1/embeddings and /v1/models (API compatibility). There is no /v1/responses, so Codex CLI hits a 404 even with the right URL and key.
Pinning an old release (0.94.0 or earlier) is technically possible, but we don't recommend it: those builds get no updates or security fixes.
What to use instead
Each of these terminal agents works with uttapen and has its own guide:
- opencode — the closest experience to Codex CLI, with full control over the model and the output ceiling.
- Crush — light and fast, configured in Bash.
- Qwen Code — set up with a handful of environment variables.
- Aider — a git-centric pair programmer.
Every model you used in Codex — openai/gpt-5 and openai/gpt-5-mini included — is available through uttapen in those tools.
If the Responses path is ever added to uttapen, this page will be updated. The full tool list is in integrations.
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