[BUG] All Gemini models fail instantly in Antigravity with HTTP 404 NOT_FOUND, while Claude works

Google Antigravity
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1

Environment:

  • Windows 10 x64
  • Google AI Pro account
  • Antigravity IDE 2.5.5
  • Official Google Antigravity extension for Visual Studio Code also tested

Issue:
Every Gemini model terminates after about 1 second with:

“Agent execution terminated due to error.”

This happens even with a minimal prompt such as:
“Only reply ‘connection normal’. Do not read, inspect, modify any project files, or execute any commands.”

Tested Gemini models:

  • Gemini 3.1 Pro
  • Gemini 3.6 Flash
  • Gemini 3.7 Flash
  • Gemini 3.8 Flash

Control test:
Claude Sonnet 4.6 and Claude Opus 4.6 work normally in the same environment.

A/B testing already completed:

  • Reproduces in Antigravity Standalone IDE
  • Reproduces in the official VS Code Antigravity extension
  • Reproduces in a completely empty workspace
  • Reproduces with multiple Google AI Pro accounts
  • No MCP server is required to reproduce
  • TUN networking tested
  • Claude works normally

Debug info from the official VS Code Antigravity extension:

Trajectory ID:
1ee61916-2948-433d-9e93-a4a4*****

Trace ID:
0x8ae1457a1****

HTTP error:
404 NOT_FOUND

Backend response:
“Requested entity was not found.”

This strongly suggests the issue is related to Gemini backend model routing/entity mapping in Antigravity rather than a local workspace or network issue.

I have also submitted an in-product Bug Report with Antigravity server logs attached.

Please investigate the above Trajectory ID and Trace ID on the Antigravity backend.

Snipaste_2026-09-02_23-26-00
Snipaste_2026-09-02_23-26-00663×1043 60 KB

3

Hi @chao_guang, Welcome to the Forum

The HTTP 404 NOT_FOUND ("Requested entity was not found") occurs at the Gemini backend model routing proxy.

Could you please try these trouble shooting steps:

  • Update to the Latest Antigravity Build (Recommended):
    • Antigravity 2.5.5 uses older model catalog definitions. Update newer releases these backend model routing schemas.
    • Please update your standalone IDE from the official Antigravity download portal and update the VS Code extension to the latest available version.
  • Purge Stale Local Cache & Reset Onboarding:
    • Close Antigravity and VS Code.
    • On Windows, delete the cached endpoint schemas by navigating to:
      • %AppData%\Antigravity\Cache
      • %AppData%\Antigravity\Code Cache
    • Re-launch the IDE, press Ctrl + Shift + P, and run: Antigravity: Reset Onboarding.
    • Sign back in with your Google AI Pro account to pull fresh model manifests from the backend.

Please let us know if updating to the latest build resolves the 404 error for you or issue still persists.