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System message must be at the beginning - Claude Code

Quick fix

Change the API format for NVIDIA Qwen, or upgrade cc-switch to v3.13.0+ to fix the 400 from providers such as Copilot.

Symptom

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

Cause

Section titled “Cause”

This cluster mixes several variants producing HTTP 400 (Bad Request). The core mechanism is the request body or auth headers the cc-switch proxy layer builds failing an upstream provider's strict validation. NVIDIA Qwen models on the openai_chat format require the system role message to be first in the messages array; older GitHub Copilot had an incompatibility between the auth header and API path detection; and when the input context exceeds the model window, the adaptation layer calculates a negative max_tokens, which also triggers an upstream 400.

Fix

Section titled “Fix”

  1. On NVIDIA Qwen models, adjust the API format setting to avoid openai_chat, or make sure the system prompt is merged correctly.

  2. On the GitHub Copilot provider, upgrade cc-switch to v3.13.0 or newer for the authentication and 400 fix.

  3. If the error mentions a negative max_token, reduce the input context in the current session so it stays within the model context window.

Affected Versions

Section titled “Affected Versions”
ToolClaude Code
Version3.12.3 - 3.16.3
PlatformsWindows

Source Issues

Section titled “Source Issues”

This page is distilled from 4 real issues

FAQ

Section titled “FAQ”
Why does picking API_KEY authentication for GitHub Copilot produce a 400?
A known defect before v3.13.0: choosing API_KEY as the auth field produces incompatible request headers. Upgrading to v3.13.0 resolves it.
What causes a negative max_token (-46551, for example)?
Your input (history plus code) exceeds the model context window (128k, say), so the adaptation layer calculates a negative max_tokens. Clear some context.
Section titled “Related problems”
EGL_BAD_PARAMETER white screen error - cc-switchInstall the native .deb or AUR package instead, or run the AppImage with LD_PRELOAD pointing at the system library, to resolve the ABI conflict.6 issues mergedConsole Go: Upstream request failedThis 400 comes from the OpenCode Go gateway rejecting an incompatible payload. Restart the proxy to restore session mapping, or avoid WebSearch and images.3 issues mergedAPI Error: 400 model_not_supportedRestart CC Switch to repair the proxy routing, or confirm whether the model ID requested became invalid after a Copilot policy change.2 issues merged

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