How to Connect Codex with DeepSeek V4 – A Complete Step‑by‑Step Guide

Protocol mismatch

Codex uses OpenAI's Responses API while DeepSeek V4 provides a Chat Completions endpoint. Because the two APIs speak different protocols, a direct connection fails.

Solution via cc-switch

Recent updates to cc-switch (version 3.16.0 or later) add a local proxy that automatically translates Codex Responses requests into DeepSeek Chat Completions calls, then rebuilds the response into the original format, preserving inference, tool calls, and streaming state.

Installation

Download the latest release (≥ 3.16.0) from https://github.com/farion1231/cc-switch. Choose the MSI installer for Windows or the DMG for macOS.

Obtain a DeepSeek API key from the DeepSeek Open Platform (https://platform.deepseek.com/api_keys). The key starts with sk‑.

Open cc-switch, switch to the Codex tab, and add a new vendor:

Open the settings panel, locate the routing tab, and turn on the three switches mentioned above.

Restart Codex (running processes do not hot‑load configuration). In the CLI run /model and verify that DeepSeek V4 appears in the model list.

Common pitfalls : forgetting to restart Codex after saving the vendor, or using a newer Codex version that fetches the model list from /models instead of the older file‑based injection used by cc-switch. In the latter case the model works even if the UI label shows “GPT”.

Solution via Codex++

Codex++ provides a graphical interface and a browser‑plugin integration.

Installation

Download the appropriate package from https://github.com/BigPizzaV3/CodexPlusPlus/releases. Choose the Windows installer or the macOS DMG matching the CPU architecture ( CodexPlusPlus-1.1.7-macos-arm64.dmg for Apple Silicon, CodexPlusPlus-1.1.7-macos-x64.dmg for Intel).

Obtain a DeepSeek API key as described above.

In Codex++ add a new supplier:

Launch Codex from the Codex++ UI; the plugin unlocks and DeepSeek V4 appears in the model selector.

Comparison

cc-switch : lightweight, minimal configuration, stable for users who prefer a low‑maintenance setup.

Codex++ : graphical UI and browser‑plugin integration, suitable for users who want visual configuration tools. May require updates when Codex releases new versions.

FAQ

DeepSeek model not visible

Ensure Codex was restarted after saving the vendor; the running process does not hot‑load changes. If the model still does not appear, the newer Codex version may be pulling the list from /models, which cc-switch does not implement. The model remains functional even if the UI label shows “GPT”.

Conversation history disappears after switching models

Codex isolates chat history by model provider. Switching to DeepSeek creates a new history view; previous sessions remain under the original provider.