Gemini API: models.list returns gemini-2.5-flash with generateContent support, but generateContent returns 404 NOT_FOUND

Gemini API
1

We are diagnosing a Gemini API request for a development project using synthetic data only.

A metadata request to GET /v1beta/models succeeds with HTTP 200 and returns a complete model list. The returned resources include:

models/gemini-2.5-flash

with supportedGenerationMethods including:

generateContent

However, a request to:

POST /v1beta/models/gemini-2.5-flash:generateContent

consistently receives:

HTTP 404
Google JSON error code 404
canonical status NOT_FOUND

The request uses x-goog-api-key authentication and Content-Type: application/json.

We have independently verified that the generated URL exactly matches the documented route and the resource returned by the Models API.

Could you clarify:

  1. What resource or operation can produce NOT_FOUND in this situation when the same credential can list the model and the model advertises generateContent?
  2. Are there project-, billing-tier-, region-, model-access-, or API-version-specific conditions that can make models.list expose a model while generateContent for that model returns NOT_FOUND?
  3. Is x-goog-api-key supported equivalently to the documented API-key authentication for this v1beta generateContent route?
  4. Is there any account/project-side setting we should verify?

We do not want to provide the API key or raw request dumps. If you need additional non-sensitive fields to identify the issue, please specify exactly which fields are required.

2

Hello @Supachai_Pad ,

To ensure reliable performance for everyone, we are limiting access to the 2.5 models to users who have actively used them in the past. These models are not deprecated and will continue to be served until further notice.
For your new projects, please use our latest models: 3.5 Flash-Lite or 3.8 Flash. This helps us maintain sufficient capacity for both ongoing legacy workflows and new applications.