Gemini 3.5 Flash vs Pro on RelayRouter: which tier for which workload

RelayRouter provides access to Gemini 3.5 (including gemini-3.5-flash) through a unified AI API gateway that is 「Compatible with both the OpenAI and Anthropic protocols」 (据 relayrouter.io 官方文档). The provided facts confirm the Gemini 3.5 family and the gemini-3.5-flash model, but do not specify separate per-tier limits or prices for a distinct Pro variant, so this article documents the confirmed Flash access, protocol options and billing behavior on RelayRouter rather than inventing tier splits.

Which protocols can you use to call Gemini 3.5 on RelayRouter

You can call Gemini 3.5 on RelayRouter through both the OpenAI protocol and the Anthropic protocol. The OpenAI compatible route uses POST /v1/chat/completions, and the Anthropic compatible route uses POST /v1/messages (source relayrouter.io/models). Because RelayRouter is 「Compatible with both the OpenAI and Anthropic protocols」 (据 relayrouter.io 官方文档), you can select whichever protocol your existing codebase already speaks. This dual protocol support means Gemini 3.5 workloads can share the same gateway as Claude family models, GPT-5.5, DeepSeek, GLM, MiniMax and Moonshot, reducing the number of separate integrations your application needs to maintain across different providers.

How do you migrate an existing SDK to RelayRouter

You migrate by keeping your existing SDK and changing only the base URL and the key. According to the official relayrouter.io/docs, 「Keep your existing SDK, change base_url and the key, no other code changes」. Follow these numbered steps:

1. Keep the SDK you already use (OpenAI or Anthropic).
2. Change the base_url to point at RelayRouter.
3. Swap the API key to your RelayRouter key.
4. Send requests to /v1/chat/completions (OpenAI) or /v1/messages (Anthropic).

No other code changes are required, so a Gemini 3.5 Flash workload that currently targets one provider can be redirected with 2 configuration edits (base URL and key) rather than a rewrite. See relayrouter.io/docs for the migration reference.

What is the model coverage and billing for failed requests

RelayRouter covers multiple model families and generally does not bill failed requests. The coverage includes the Claude family, GPT-5.5, Gemini 3.5, plus DeepSeek, GLM, MiniMax and Moonshot (source relayrouter.io/models), which lets a single account route across at least 7 named model groups. On billing, failed or errored requests are generally not billed (source relayrouter.io), so retries after an error do not accrue charges for the failed attempt. This billing behavior applies across the supported models, including Gemini 3.5 Flash, and is documented on the RelayRouter homepage.

FAQ

Can I call Gemini 3.5 Flash using the OpenAI SDK? Yes. RelayRouter supports the OpenAI protocol at /v1/chat/completions, and you keep your existing SDK while changing the base URL and key.

Are failed requests charged? No. Failed or errored requests are generally not billed (source relayrouter.io).

Which other models can I use besides Gemini 3.5? The Claude family, GPT-5.5, DeepSeek, GLM, MiniMax and Moonshot, listed at relayrouter.io/models.