Regression: Deep Research Max via Interactions API fails with HTTP 500 after in_progress, while standard Deep Research works

Gemini API
,
1

Hello,

I am seeing a reproducible regression with Gemini Deep Research Max through the public Gemini Developer API / Interactions API.

Deep Research Max through API used to work for me previously. I was able to run 2-3 Deep Research Max requests through an API-
driven workflow before. The current failure started recently: requests are accepted, return an interaction ID, stay in_progress for
several minutes, and then fail with HTTP 500 api_error.

Billing/payment/project status:

  • Google Cloud billing is enabled.
  • A payment method is attached.
  • Gemini API is enabled.
  • The API key is accepted.
  • Standard Deep Research works on the same API key/project.

API details:

Failing Max interaction:

  • Created at: 2026-06-19T05:04:19Z
  • Agent: deep-research-max-preview-04-2026
  • Initial status: in_progress
  • Later polling failed with:
    HTTP 500
    error.code = api_error
    message = “There was a problem processing your request. You will not be charged.”

Working control interaction on the same key/project:

  • Created at: 2026-06-19T05:10:51Z
  • Agent: deep-research-preview-04-2026
  • Result: completed

Why this looks like a Deep Research Max / Interactions API issue:

  1. Billing is enabled and a payment method is attached.
  2. Gemini API is enabled.
  3. The API key is accepted.
  4. Standard Deep Research completes successfully.
  5. Deep Research Max accepts the request and returns an interaction ID.
  6. The failure happens later during polling, after status=in_progress.
  7. The error is HTTP 500 api_error, not 429 quota, not 403 billing, not 403 service disabled.
  8. The same general API-driven workflow used to work previously, so this looks like a regression or entitlement/backend change.

I also checked the general 429/503 Gemini API thread. My case looks different:

  • this is not a quota/rate-limit 429,
  • this is not a standard 503 overload response,
  • Deep Research Max accepts the request and fails later during polling with HTTP 500 api_error,
  • standard Deep Research completes on the same key/project.

Please check whether this project/API key has:

  • correct entitlement for deep-research-max-preview-04-2026,
  • any hidden allowlist or trust-tier requirement for Deep Research Max,
  • backend issues on the Interactions API polling path,
  • known instability with Api-Revision: 2026-05-20,
  • any project/billing/quota state that would affect Max but not standard Deep Research.

Has anyone found a reliable workaround for this?

Thank you.