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400 content[].thinking must be passed back - Claude Code

Quick fix

Upgrade cc-switch to v3.15.0 or newer to fix lost thinking blocks, or downgrade Claude Code and use the native DeepSeek Anthropic endpoint.

Symptom

Section titled “Symptom”
Error output
API Error: 400 The `content[].thinking` in the thinking mode must be passed back to the API.

Cause

Section titled “Cause”

With extended thinking on, Claude Code and Codex require the previous turn's thinking or reasoning_content block to be passed back verbatim in the next request. In versions before v3.15.0, the cc-switch protocol conversion layer failed to preserve or pass those blocks correctly, so upstream rejected the request with a 400. Different models (Kimi, for example) also expect different formats for the thinking parameter, producing similar 400s.

Fix

Section titled “Fix”

  1. Upgrade cc-switch to v3.15.0 or newer; maintainers fixed the reasoning_content format conversion in that version.

  2. If it still errors after upgrading, downgrade Claude Code to v2.1.150 or earlier (v2.1.119, for example) to work around it: npm install -g @anthropic-ai/[email protected]

  3. For DeepSeek models, configure the native Anthropic-compatible endpoint in cc-switch rather than the OpenAI-compatible one, avoiding unnecessary format conversion.

Affected Versions

Section titled “Affected Versions”
ToolClaude Code / Codex
Versioncc-switch < 3.15.0 (affected), >= 3.15.0 (fixed)
PlatformsWindows

Source Issues

Section titled “Source Issues”

This page is distilled from 4 real issues

FAQ

Section titled “FAQ”
How do I go back to an older Claude Code and turn auto-upgrade off?
No need to uninstall first — installing a specific version through npm overwrites and downgrades it: npm install -g @anthropic-ai/[email protected].
Why does DeepSeek error through the OpenAI-compatible endpoint?
DeepSeek offers a native Anthropic endpoint. Going through the OpenAI-compatible one triggers cc-switch format conversion, which readily loses data in thinking mode. Use the Anthropic endpoint directly.
Section titled “Related problems”
Body text appears in thinking blocks, visible text nearly emptyUpgrade cc-switch to a build with PR #4210. Reactive thinking-placeholder handling fixes long-context freezes and body-text collapse.1 issues mergedAPI Error: 400 Param Incorrect Claude CodeUpgrade CC Switch to v3.16.2+ to fix 400 errors caused by missing reasoning_content in MiMo thinking mode.2 issues mergedInvalid schema for function 'codex_app__automation_update'Upgrade cc-switch to v3.18.0+ to fix upstream HTTP 400 errors caused by missing type: object in Codex tool parameters.5 issues merged

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