Gemini-3.8-flash and gemini-3.1-flash-lite intermittently return 400 "does not support background interactions"

Gemini API
1

On 2026-09-21, the Interactions API briefly rejected background execution for gemini-3.8-flash and gemini-3.1-flash-lite. The same request shape succeeded earlier that day and succeeds again now. The public docs still list these models as supported.

Endpoint
POST https://generativelanguage.googleapis.com/v1beta/interactions
Header: Api-Revision: 2026-05-20

Request shape
{
“model”: “gemini-3.8-flash” | “gemini-3.1-flash-lite”,
“background”: true,
“store”: true,
“generation_config”: { “temperature”: 0.1 },
“response_format”: { “type”: “text”, “mime_type”: “application/json”, “schema”: { … } },
“webhook_config”: { “uris”: [“example”], “user_metadata”: { … } },
“system_instruction”: “…”,
“input”: “…”
}

Timeline (UTC)

  • 2026-09-21 14:50: the same client and request shape created background interactions for both models, and those interactions completed.
  • 2026-09-21 20:55–21:10: creates failed with HTTP 400:
    {“error”:{“message”:“Model ‘gemini-3.8-flash’ does not support background interactions.”,“code”:“invalid_request”}}
    {“error”:{“message”:“Model ‘gemini-3.1-flash-lite’ does not support background interactions.”,“code”:“invalid_request”}}
    No client change was deployed between the successful calls and these failures. Some creates in the same window were accepted and returned an interaction id, then the interaction was later reported failed.
  • 2026-09-22 02:40: the same request shape, including JSON schema and webhook_config, is accepted again for both models and returns status “in_progress”.

Docs
https://ai.google.dev/gemini-api/docs/background-execution (last updated 2026-09-17) says background execution is supported for standard Gemini models such as gemini-3.8-flash. The webhook guide also uses gemini-3.8-flash with background: true. The changelog has no notice that these models lost background support.

Please confirm whether this was an incident, and publish which models currently support background interactions. The 400 text says the model does not support the feature, which is not the same as a transient outage.

2

I’m getting the same on Gemini 3.5-flash-lite; can’t find a concrete list of which models should support backgrounding or not. What’s odd is 3.8-flash and 3.1-flash-lite both work for me

POST https://generativelanguage.googleapis.com/v1beta/interactions
x-goog-api-key: <redacted>
api-revision: 2026-05-20
Content-Type: application/json

Request:
{"model":"gemini-3.5-flash-lite","input":"Reply with the word ok.","background":true}

Response:
{"error":{"message":"Model 'gemini-3.5-flash-lite' does not support background interactions.","code":"invalid_request"}}

And when I tried with 3.8 flash or even 3.1 flash lite (Response):
{"id":"v1_Chc0NXF5...","status":"in_progress","created":"2026-09-22T15:12:35Z","service_tier":"standard","object":"interaction","model":"gemini-3.1-flash-lite"}
3

Hello all,

Thank you for letting us know. We are looking into this.