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System message must be at the beginning.: Claude Code

Quick fix

Change Claude Code's "model" from "opus" to "haiku" or another model family to avoid an OpenAI-compatible API 400 response.

Symptom

Section titled “Symptom”
Error output
API Error: 400 System message must be at the beginning.

Cause

Section titled “Cause”

When cc-switch proxies an OpenAI-compatible chat API, requests from Claude Code using the "opus" model family retain a system message that is not first. The backend requires role: system to be the first item in the messages array, so it rejects the request with 400.

In this issue, the "haiku" model family uses a different message-building path, where the system message happens to be first, so the session works normally. The issue suggests cc-switch should normalize system-message order when converting Anthropic requests to OpenAI Chat Completions, but the issue remains open.

Fix

Section titled “Fix”

  1. In Claude Code's cc-switch configuration, change "model" from "opus" to "haiku", or use another model family.

  2. Restart the Claude Code session and confirm that this 400 error no longer appears.

Affected Versions

Section titled “Affected Versions”
ToolClaude Code
Version3.20.4（受影响版本）
PlatformsmacOS

Source Issues

Section titled “Source Issues”

This page is distilled from 1 real issues

FAQ

Section titled “FAQ”

(No FAQ yet)

Section titled “Related problems”
<thinking> tags output as body text in Claude CodeChanging the provider's apiFormat from openai_chat to anthropic, if supported upstream, can bypass inline <thinking> leakage.1 issues mergedIncorrect model displayed in Claude CodeConfigure a Custom Command for ccstatusline to read the model name from the current cc-switch provider configuration.1 issues mergedInvalid messages.content.type Parameter Claude CodeMost related issues remain unresolved. Upgrade to a version containing the #7656 fix so Chinese image-rejection errors trigger image fallback retries.1 issues merged

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