Linking GCP billing account does not upgrade Gemini API from free-tier quotas

[quotentiroler]

Problem

After linking a GCP billing account (with active credits) to a project, the Gemini API continues to enforce free-tier quotas (generate_content_free_tier_requests, limit: 20 req/day/model). There is no indication in any UI that billing linkage didn't actually upgrade the API tier.

Steps to Reproduce

1. Create a GCP project
2. Link a billing account with active credits
3. Enable the Generative Language API
4. Create an API key from the project credentials page
5. Make API calls to gemini-3-flash-preview via @google/genai SDK
6. After hitting 20 requests → still get free-tier quota error:

Quota exceeded for metric: generativelanguage.googleapis.com/generate_content_free_tier_requests
quotaId: GenerateRequestsPerDayPerProjectPerModel-FreeTier

Expected Behavior

Linking a billing account with active credits should upgrade the project from free-tier to pay-as-you-go quotas, or at minimum clearly indicate that additional steps are required to enable paid usage.

Actual Behavior

• GCP Console shows billing is linked
• API quota page still shows free tier quotas at 100% usage
• No error, warning, or guidance anywhere that billing isn't effective for Gemini API keys
• Significant time wasted debugging what appeared to be a correctly configured setup

Impact

Developers who follow the standard GCP flow (create project → link billing → create key) reasonably expect paid quotas to apply. The silent failure to upgrade tiers, combined with zero UI feedback, creates a frustrating developer experience.