Bug Description
When using the gemini-3-pro-preview or gemini-3-flash-preview models in n8n via Vertex AI Node, the workflow crashes during Function Calling.
While standard chat interactions work, any attempt by the model to use a connected Tool/Agent results in a Bad request Error regarding missing thought_signatures.
Error message:
Unable to submit request because function call default_api: in the 2. content block is missing a thought_signature. Learn more: https://docs.cloud.google.com/vertex-ai/generative-ai/docs/thought-signatures
This does not occur with other Gemini models like gemini-2.5-flash.
The issue was also reported in some earlier versions of n8n:
https://community.n8n.io/t/issue-with-gemini-3-0-gemini-3-pro-preview-tools-function-call-is-missing-a-thought-signature/223824
To Reproduce
Create a new workflow with an AI Agent node.
Select the Google Vertex AI Node.
Set the Model ID to gemini-3-pro-preview or gemini-3-flash-preview.
Connect a Tool.
Send a prompt that forces the agent to use the tool.
The node fails immediately after the model attempts to generate the function call.
Expected behavior
The agent should be able to process the "thought_signature" generated by Gemini 3 and pass it back to the API along with the function call.
https://docs.cloud.google.com/vertex-ai/generative-ai/docs/thought-signatures
Debug Info
Debug info
core
- n8nVersion: 2.0.3
- platform: docker (self-hosted)
- nodeJsVersion: 22.21.0
- nodeEnv: production
- database: sqlite
- executionMode: regular
- concurrency: -1
- license: enterprise (production)
- consumerId: 2c7cd698-b0f6-46b3-b8fa-dcfc11deb037
storage
- success: all
- error: all
- progress: false
- manual: true
- binaryMode: filesystem
pruning
- enabled: true
- maxAge: 336 hours
- maxCount: 10000 executions
client
- userAgent: mozilla/5.0 (windows nt 10.0; win64; x64) applewebkit/537.36 (khtml, like gecko) chrome/143.0.0.0 safari/537.36
- isTouchDevice: false
Generated at: 2026-01-02T16:40:13.114Z
Operating System
Raspberry Pi OS
n8n Version
2.0.3
Node.js Version
22.21.0
Database
SQLite (default)
Execution mode
main (default)
Hosting
self hosted
Bug Description
When using the gemini-3-pro-preview or gemini-3-flash-preview models in n8n via Vertex AI Node, the workflow crashes during Function Calling.
While standard chat interactions work, any attempt by the model to use a connected Tool/Agent results in a Bad request Error regarding missing thought_signatures.
Error message:
Unable to submit request because function call default_api: in the 2. content block is missing a thought_signature. Learn more: https://docs.cloud.google.com/vertex-ai/generative-ai/docs/thought-signatures
This does not occur with other Gemini models like gemini-2.5-flash.
The issue was also reported in some earlier versions of n8n:
https://community.n8n.io/t/issue-with-gemini-3-0-gemini-3-pro-preview-tools-function-call-is-missing-a-thought-signature/223824
To Reproduce
Create a new workflow with an AI Agent node.
Select the Google Vertex AI Node.
Set the Model ID to gemini-3-pro-preview or gemini-3-flash-preview.
Connect a Tool.
Send a prompt that forces the agent to use the tool.
The node fails immediately after the model attempts to generate the function call.
Expected behavior
The agent should be able to process the "thought_signature" generated by Gemini 3 and pass it back to the API along with the function call.
https://docs.cloud.google.com/vertex-ai/generative-ai/docs/thought-signatures
Debug Info
Debug info
core
storage
pruning
client
Generated at: 2026-01-02T16:40:13.114Z
Operating System
Raspberry Pi OS
n8n Version
2.0.3
Node.js Version
22.21.0
Database
SQLite (default)
Execution mode
main (default)
Hosting
self hosted