Configure OpenAI Codex CLI to use DeepSeek models

codex-deepseek-setup.md

Configure OpenAI Codex CLI with DeepSeek Support

⚠️ No Longer Working (January 2026): This configuration was working when originally created, but is now broken due to Codex deprecating the Chat Completions API (wire_api = "chat") in favor of OpenAI's Responses API. Since DeepSeek only supports Chat Completions, this integration no longer works reliably. Tool calls fail with message format errors.

What Happened

• Before: DeepSeek worked with Codex using wire_api = "chat"
• Now: Codex is deprecating wire_api = "chat", and the code path has bugs that won't be fixed
• Result: Tool calls fail with errors like "insufficient tool messages following tool_calls message"

Original Configuration (was working)

~/.codex/config.toml

# Default model - OpenAI
model = "gpt-5.1-codex"

# DeepSeek provider definitions
[model_providers.deepseek]
name = "DeepSeek"
base_url = "https://api.deepseek.com/v1"
env_key = "DEEPSEEK_API_KEY"
wire_api = "chat"

[model_providers.deepseek-reasoner]
name = "DeepSeek Reasoner"
base_url = "https://api.deepseek.com/v1"
env_key = "DEEPSEEK_API_KEY"
wire_api = "chat"

# Profile for DeepSeek Chat (V3.2 non-thinking)
[profiles.deepseek]
model = "deepseek-chat"
model_provider = "deepseek"

# Profile for DeepSeek Reasoner (V3.2 thinking mode)
[profiles.deepseek-r1]
model = "deepseek-reasoner"
model_provider = "deepseek-reasoner"

Usage (when it was working)

# Default - uses OpenAI gpt-5.1-codex
codex

# Switch to DeepSeek V3.2 Chat
codex --profile deepseek
codex -p deepseek

# Switch to DeepSeek V3.2 Reasoner
codex --profile deepseek-r1
codex -p deepseek-r1

Setup

1. Set your DeepSeek API key:

export DEEPSEEK_API_KEY="your-deepseek-api-key"

2. Add to your shell profile (~/.bashrc, ~/.zshrc, etc.):

export DEEPSEEK_API_KEY="your-deepseek-api-key"

3. Place the config in ~/.codex/config.toml

Current Errors (January 2026)

# Deprecation warning
Support for the "chat" wire API is deprecated and will soon be removed.

# Tool call error
An assistant message with 'tool_calls' must be followed by tool messages 
responding to each 'tool_call_id'. (insufficient tool messages following 
tool_calls message)

# Reasoner error
Missing `reasoning_content` field in the assistant message

Alternatives

Since Codex + DeepSeek no longer works, consider:

• OpenAI models with Codex - fully supported
• Aider - native DeepSeek support
• Continue - native DeepSeek support
• DeepSeek API directly - full control

References

• DeepSeek API Docs
• DeepSeek Models & Pricing
• OpenAI Codex CLI

seeing this error

{"error":{"message":"Missing `reasoning_content` field in the assistant message at message index 7. For more information, please refer to https://
api-docs.deepseek.com/guides/thinking_mode#tool-calls","type":"invalid_request_error","param":null,"code":"invalid_request_error"}}

Same as @megtog

Same as @megtog . so which one could run?

I've updated the gist @megtog @CharlieBytesX @yyy1mu
There was a deprecation from OpenAI side, let me know if it works for you.

Also, now the config is cleaner

My bad @megtog @CharlieBytesX @yyy1mu
It seems Codex is not compatible anymore with DeepSeek... We might submit a bug to OpenAI maybe...