Gemini-3-flash-preview: "Tool use with function calling is unsupported" when combining fileSearch with functionDeclarations (worked last week)

Gemini API
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1

When combining fileSearch (FileSearchStore) with functionDeclarations in the same request to gemini-3-flash-preview, the API now returns:

Tool use with function calling is unsupported by the model.

This was working as recently as last week (~Feb 9). We haven’t changed our implementation — the model appears to have been updated behind the same gemini-3-flash-preview identifier.

Our Setup

We send a tools array containing both:

[
{ “functionDeclarations”: [{ “name”: “create_task”, … }, { “name”: “get_users”, … }] },
{ “fileSearch”: { “file_search_store_names”: [“projects/xxx/fileSearchStores/yyy”] } }
]

This allows our agent to search uploaded user documents (via RAG) while also taking actions through custom function calls. The two tool types worked together fine until this past week.

Question

Is this a regression, or is combining fileSearch with functionDeclarations intentionally unsupported going forward? The Gemini 3 docs mention “combining built-in tools with function calling is not yet supported” — but this was working, so we’re unsure if it’s a temporary limitation or a permanent restriction.

If it’s intentional, are there plans to support this combination? Our use case (RAG + function calling in the same agent turn) seems like a common agentic pattern.

Related

  • gemini-3-flash-preview file search returns empty content (works in 2.5)
  • File Search Tool in combination with response schema not working
2 Likes
2

i have the same problem. is there any way t osolve this?

3

My hotfix was to basically create a sub-agent flow that that sole purpose is only search. Then I wrapped this code-flow and registered it as a functionDeclaration to my base-agent. That function has one argument which is prompt, that basically says include relevant context for search.

It feels wrong to have to do this b/c of round trip added :person_shrugging:

4

any hope google will fix this or why this even happens?

5

Same issue here. Was working until Fev 14 2026.

I am using gemini-3-flash-preview or gemini-3-pro-preview.

Both failed now (in a production environnement ! )

6

Have you also been unable to find a solution to this problem yet?

7

No solution. I deactivated fileSearch for the moment

8

@Mustan_lokhand Here is another API inconsistent behavior. I would really appreciate it if the team at large has a chance to respond here.

3 Likes
9

@Benjamin_Nappier thank you for flagging this, our team is looking into this

2 Likes
10

Will it be fixed? It is very important.

11

I just started getting “Built-in tools ({google_search}) and Custom tools (Function Calling) cannot be combined in the same request. Please choose one to continue.” errors. Looks like this is breaking things elsewhere too: v4.1.28 HTTP 400: Built-in tools ({google_search}) and Custom tools (Function Calling) cannot be combined in the same request. Please choose one to continue. · Issue #2241 · lbjlaq/Antigravity-Manager · GitHub

12

@Mustan_lokhand Could someone from the Google Team please explain why these API features cannot be used compositionally. On the backend, couldn’t these different ‘tools’ effectively be run in parallel?

It kills API performance to have to do them sequentially.

2 Likes
13

@Mustan_lokhand Sorry if the ping is noisy. I would love an update. The timing of doing file-search followed by another llm-round trip for function calls synchronously is really killing our user-experience right now.

14

Tool use with function calling again working?