HTTP 404 Not Found when using Claude Opus 4.6 in Antigravity despite active Google AI Pro subscription

Google Antigravity
1

I encountered a persistent HTTP 404 Not Found error while trying to use Claude Opus 4.6 inside Antigravity.

Important account detail:
I have an active Google AI Pro subscription, so this issue does not appear to be caused by lack of subscription access on my side.

The issue appears to happen during model access/request execution, and the response indicates that the requested entity could not be found. This suggests that the selected model endpoint, model mapping, or backend route may be incorrect, unavailable, or no longer valid.

Error Details:
Trajectory ID: 7f57ea5c-13f2-4e8a-82aa-b748a3c…
Trace ID: 0x69311122c0f…
HTTP Status: 404 Not Found

Raw Error Response:
{
“error”: {
“code”: 404,
“message”: “Requested entity was not found.”,
“status”: “NOT_FOUND”
}
}

Headers:
{
“Alt-Svc”: [“h3=\”:443\“; ma=2592000,h3-29=\”:443\“; ma=2592000”],
“Content-Length”: [“114”],
“Content-Type”: [“text/event-stream”],
“Date”: [“Wed, 11 Mar 2026 19:20:39 GMT”],
“Server”: [“ESF”],
“Server-Timing”: [“gfet4t7; dur=524”],
“Vary”: [“Origin”, “X-Origin”, “Referer”],
“X-Cloudaicompanion-Trace-Id”: [“69311122c0f8ec4d”],
“X-Content-Type-Options”: [“nosniff”],
“X-Frame-Options”: [“SAMEORIGIN”],
“X-Xss-Protection”: [“0”]
}

What I was doing:

  • Opened Antigravity
  • Selected Claude Opus 4.6
  • Attempted to use the model
  • Received HTTP 404 Not Found

Expected Behavior:
Claude Opus 4.6 should either:

  • work normally if supported, or
  • show a clear entitlement/availability message if it is not available for my account

Actual Behavior:
The request fails with:
“Requested entity was not found.”

Why this seems incorrect:
Since I already have an active Google AI Pro subscription, a 404 NOT_FOUND response suggests this may be a backend model mapping issue, invalid model identifier, removed endpoint, or stale UI listing rather than a normal subscription/access problem.

Request:
Please verify whether Claude Opus 4.6 is currently supported and correctly mapped in Antigravity, and check why the request returns 404 NOT_FOUND instead of a normal response or a clearer unsupported-access message.

2

Hi @Adnan_Kattaa,

Thank you for reporting this. I have checked on my end and it is working for me.

To help us understand why you are seeing this 404 error, could you please confirm:

  • What version of Antigravity are you currently using?
  • Does the model appear as ‘Claude Opus 4.6’ or ‘Claude Opus 4.6 (Thinking)’ in your selector?
  • Does switching to a different model (like Gemini 3.1 Pro) work normally for you?
3

Hello,

Thank you for your response.

Here are the details you asked for:

• Antigravity Version: 1.20.5

• The error appears only when I select the model “Claude Opus 4.6”.

• When I switch to “Gemini 3.1 Pro”, everything works normally and no 404 error appears.

• I did not test “Claude Opus 4.6 (Thinking)”, but the issue consistently occurs with the standard “Claude Opus 4.6”.

Please let me know if you need any additional information or logs.

Best regards.

4

Hi @Adnan_Kattaa,

• The error appears only when I select the model “Claude Opus 4.6”.

Could you please clear the cache and provide a screenshot of the model selector?