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Bad request (400) Claude Code

Quick fix

Upgrade CC Switch to v3.16.3; the new health check treats HTTP 400 as provider reachability.

Symptom

Section titled “Symptom”
Error output
弹出黄色警告：Xiaomi MiMo T1 检查被拒: Bad request (400)，提示 供应商拒绝了请求格式。健康检查的探测格式可能与实际使用不同。
English translation

A yellow warning appears: Xiaomi MiMo T1 check rejected: Bad request (400). It says the provider rejected the request format. The health-check probe format may differ from actual use.

Cause

Section titled “Cause”

Before v3.16.3, the health check sent a real model request. Third-party gateways such as Xiaomi MiMo may reject this probe format with 400, 403, or WAF, causing a false unavailable report; in this report, sending a request to `/anthropic/v1/messages` returned HTTP 200.

The maintainer explained that v3.16.3 changed to a lightweight reachability probe for `base_url`: any HTTP response, including 400, 4xx, and 5xx, is treated as reachable. Only DNS, connection, TLS, or timeout failures are treated as unreachable.

Fix

Section titled “Fix”

  1. Upgrade CC Switch to v3.16.3.

  2. After upgrading, click the Xiaomi MiMo provider’s “Test” button again to confirm the health-check result.

Affected Versions

Section titled “Affected Versions”
ToolClaude Code
Versionv3.16.3（已修复）
PlatformsWindows

Source Issues

Section titled “Source Issues”

This page is distilled from 1 real issues

FAQ

Section titled “FAQ”
Is codex takeover of local routing enabled in settings?
The maintainer concluded that the health-check probe format was rejected by the gateway; after upgrading to v3.16.3, it uses a lightweight reachability probe.
Section titled “Related problems”
Unknown name "prompt_cache_key" - cc-switchUpgrade cc-switch to v3.16.2+ to fix prompt_cache_key injection, or use an OpenRouter endpoint that natively speaks the Claude Code format.6 issues merged401 UnauthorizedUpgrade to cc-switch 4.0.x, or clear the stale third-party OPENAI_API_KEY from ~/.codex/auth.json manually, restart Codex, and sign in again with ChatGPT OAuth.2 issues mergedMissing API key.：Claude Desktop OpenCode GoChange the upstream authentication field from ANTHROPIC_AUTH_TOKEN to ANTHROPIC_API_KEY so requests are sent through x-api-key.4 issues merged

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