TOS Check: BYOK middleware for automated Flex Tier and Context Caching

Gemini API
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Hi everyone,

I’m an independent developer researching cost-optimization architectures for generative AI. I’m currently designing a local middleware (API gateway) to sit between client apps and the Gemini API (generativelanguage.googleapis.com), and I want to do a quick sanity check to ensure this approach is fully compliant with the Terms of Service.

The Architecture:

  • BYOK (Bring Your Own Key): The middleware operates strictly using the end-user’s provided API key.

  • Flex Tier Injection: It intercepts standard requests and automatically injects the service_tier: "flex" parameter to route traffic to the cost-optimized queue.

  • Context Caching Optimization: It restructures payloads (e.g., front-loading static instructions) to maximize Implicit Context Caching hits, or explicitly calls the Context Caching API for large contexts.

  • Zero Data Retention (ZDR): It does not store or log any user prompts or generated responses.

Compliance Context: To be fully transparent, the sole goal here is to automate the use of Google’s officially documented cost-saving features.

  • It does not bypass any authentication mechanisms.

  • It does not evade rate limits, quotas, or billing (all traffic is strictly subject to the quotas of the user’s provided API key).

  • It does not simulate multiple accounts to circumvent billing (which I know is strictly prohibited under Section 3.3).

My Questions:

  1. Could anyone from the Google team, or fellow developers who have built similar tools, confirm if this automated BYOK middleware approach is acceptable and fully compliant with developer policies for production use?

  2. For my own learning, I’d love to hear how Google views this kind of architecture. Is building this type of cost-optimizing middleware considered a “good practice” from your perspective, or are there alternative approaches you would recommend?

  3. Lastly, I have a quick question about the business model. If this middleware successfully reduces the end-user’s direct API costs, would it be considered acceptable (and compliant with the TOS) to charge a service fee or commission based on the savings generated?

Thanks in advance for your time and insights!