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deepseek check failed: Not found (404), the endpoint does not exist - Codex

Quick fix

Codex needs the Responses API while DeepSeek only supports the Chat API — use a third-party proxy to convert between the protocols.

Symptom

Section titled “Symptom”
Error output
deepseek 检查失败: Not found (404)接口地址不存在，请检查 Base URL 和 API 路径。
English translation

deepseek check failed: Not found (404), the endpoint does not exist. Check the Base URL and API path.

Cause

Section titled “Cause”

Codex natively uses the OpenAI Responses API format while DeepSeek models only support the standard Chat Completions API. Configuring DeepSeek for Codex directly in cc-switch means the requests Codex sends are rejected by DeepSeek with a 404 or 400. cc-switch does not yet include this protocol conversion officially (tracked by #2461). The community also reports that even with a third-party conversion, unstable JSON serialisation can leave the DeepSeek prefix cache hit rate extremely low, spiking costs and misbehaving sub-agents.

Fix

Section titled “Fix”

  1. Deploy a third-party protocol conversion proxy (codex-deepseek, for example) that converts the OpenAI Responses API to the DeepSeek Chat Completions API in real time.

  2. In cc-switch, change the DeepSeek API endpoint to the local proxy address (http://127.0.0.1:15721/v1, for example).

Affected Versions

Section titled “Affected Versions”
ToolCodex
Version26.422.71525 - 26.623.61825
PlatformsWindows

Source Issues

Section titled “Source Issues”

This page is distilled from 4 real issues

FAQ

Section titled “FAQ”
Why is the DeepSeek prefix cache hit rate still low and the cost still spiking after using a conversion proxy?
Because the Responses-to-Chat format conversion can make byte-level JSON serialisation unstable, breaking the exact prefix cache DeepSeek relies on. That is a known defect in the conversion layer today.
When will cc-switch support DeepSeek protocol conversion natively?
That request is tracked in official issue #2461. Until then, use codex-deepseek, ccx, or a similar third-party tool as an interim solution.
Section titled “Related problems”
cc-switch DeepSeek usage statistics inaccurate / balance query failsUpgrade to v3.19.2 and rebuild Codex usage. The balance query needs a correct {{apiKey}}, or a proxy.17 issues mergedThe proxy takeover claude switch cannot be ticked in Claude Desktop modeIn claude-desktop mode, the takeover section hard-codes the Claude Code (claude) switch instead of the Claude Desktop one, so clicking does nothing.2 issues mergedThe apply_patch tool is unavailable with the Codex proxy onUpgrade to cc-switch v3.16.2 or newer. On a relay, make sure the backend model matches what Codex expects or tool calls fail with routing on.2 issues merged

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