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Function call is missing a thought_signature - Claude Code

Quick fix

Triggering a tool call with Gemini Native in Claude Desktop proxy mode loses the thought_signature to a session ID mismatch. Await the official fix.

Symptom

Section titled “Symptom”
Error output
API Error: 400 Function call is missing a thought_signature in functionCall parts.

Cause

Section titled “Cause”

In cc-switch v3.16.0 through v3.16.3, calling a Gemini Native model through the proxy mode of Claude Desktop or the Claude App and triggering a tool call (default_api:Bash or an MCP tool) produces an HTTP 400. The root cause is that the Gemini shadow replay mechanism keys on (provider_id, session_id), but a Claude Desktop tool call request may not supply a stable client session id. cc-switch then records the assistant turn under one generated session key while the later tool result request uses a different key, so the stored thoughtSignature cannot be recovered and the upstream Gemini returns 400. This was marked in #4492 as a duplicate of #5415.

Fix

Section titled “Fix”

  1. The problem is not fixed as of v3.16.3. Since this is a known cc-switch bug handling Gemini Native multi-turn tool calls, follow the main Issue #5415 for progress on a fix.

Affected Versions

Section titled “Affected Versions”
ToolClaude Code / Claude Desktop
Version3.16.0 - 3.16.3
PlatformsmacOS

Source Issues

Section titled “Source Issues”

This page is distilled from 2 real issues

FAQ

Section titled “FAQ”
The v3.16.0 changelog says the thought_signature problem was fixed — why do I still hit it?
v3.16.0 fixed some scenarios, but a tool call in Claude Desktop proxy mode (Bash, Glob, or an MCP tool) has an unstable session id and takes a code path that fix did not cover, so the problem remains.
Section titled “Related problems”
Failed to parse Hermes configUpgrade cc-switch to v3.16.3+ to fix the CRLF-driven config append bug, or delete the duplicate keys in config.yaml by hand.6 issues mergedFunction call is missingUse the community cc-switch-gemini-fixer patch, or inject skip_thought_signature_validator into history messages, to bypass the signature validation.3 issues mergedGtk-CRITICAL: gtk_widget_get_scale_factor failedOn a GTK assertion failure running cc-switch under Linux or WSL2, edit settings.json to turn silent startup off, or clean the leftovers and reinstall.3 issues merged

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