Vertex AI
chat-bison model retirement
Stopped workingSubscribe to Vertex AIShare
Calls to the model chat-bison on Vertex AI stopped working on April 21, 2025.
The error you get
What Vertex AI answers a call to chat-bison once the model is gone, as recorded from real responses:
{"error":{"code":404,"message":"Publisher model `projects/{project}/locations/{region}/publishers/google/models/chat-bison` was not found or your project does not have access to it. Ensure you are using a valid model name and that the model is available in the specified region.","status":"NOT_FOUND"}}What to use instead of chat-bison
Move to gemini-3.8-flash. gemini-2.5-flash-lite, named first, stopped working on 2026-10-20.
In Vertex AI's words
Model ID: chat-bison; Release date: May 2023; Retirement date: April 21, 2025; Recommended upgrade: gemini-2.5-flash-lite
Facts
- API
- Vertex AI
aiplatform.googleapis.com - Model
chat-bison- Kind
- Model retirement
- Takes effect
- April 21, 2025
- Calls after that day
- Fail
- Source
- Deprecations page
- Last updated
- Verified
- , against Vertex AI's own pages
Questions
When does chat-bison shut down?
Calls to the model chat-bison on Vertex AI stopped working on April 21, 2025.
What happens to calls after April 21, 2025?
They have failed since April 21, 2025.
What error does chat-bison return once it is shut down?
Vertex AI answers HTTP 404: "Publisher model `projects/{project}/locations/{region}/publishers/google/models/chat-bison` was not found or your project does not have access to it. Ensure you are using a valid model name and that the model is available in the specified region.". Send another model to fix it.
How do I find the calls this hits in my code?
Okapi reads your repository, finds the calls this change hits and opens a pull request with the fix. It never commits to your branches: every change comes as a pull request you review.
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You fixed this one by hand.
Okapi opens the pull request with the fix before the next breaking change reaches your code.