ChatOpenAI fails thought signatures with Gemini multi-turn conversations — 400 BadRequestError

What this error means

ChatOpenAI fails to provide thought signatures on multi-turn conversations when used with Gemini models, resulting in 400 BadRequestError is a LangChain failure pattern reported for developers trying to fix langchain chatopenai integration producing invalid thought signatures for google gemini model responses in conversation history. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

LangChain LangChain #37347 (2026-05-11): Multi-turn Gemini conversations break when ChatOpenAI’s thought-signature feature generates incompatible formatting. Results in 400 BadRequestError blocking chat flows. Category: AI Coding Tools (LangChain framework error affecting paid AI workflows). New distinct error.

Common causes

• LangChain LangChain #37347 (2026-05-11): Multi-turn Gemini conversations break when ChatOpenAI’s thought-signature feature generates incompatible formatting. Results in 400 BadRequestError blocking chat flows. Category: AI Coding Tools (LangChain framework error affecting paid AI workflows). New distinct error.

Quick fixes

1. Confirm the exact error signature matches ChatOpenAI fails to provide thought signatures on multi-turn conversations when used with Gemini models, resulting in 400 BadRequestError.
2. Check the LangChain account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/langchain-ai/langchain/issues/37347

Evidence note: LangChain LangChain #37347 (2026-05-11): Multi-turn Gemini conversations break when ChatOpenAI’s thought-signature feature generates incompatible formatting. Results in 400 BadRequestError blocking chat flows. Category: AI Coding Tools (LangChain framework error affecting paid AI workflows). New distinct error.

Related errors

• AI Coding Tools

FAQ

What should I check first?

Start with the exact ChatOpenAI fails to provide thought signatures on multi-turn conversations when used with Gemini models, resulting in 400 BadRequestError text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed LangChain workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without ChatOpenAI fails to provide thought signatures on multi-turn conversations when used with Gemini models, resulting in 400 BadRequestError.