Sonnet 5 vs Gemini 3.1 Pro
Two models aimed at the same job: the boring-but-critical middle. RAG, chat, structured output, batch inference. Both sit on one key here, so you can settle it empirically instead of arguing.
Gemini 3.1 Pro is not currently callable on llmrelay — our upstream advertises the id but every request comes back 503 "no available Gemini accounts". We verified that four times on 2026-07-30, so we are not quoting it a price or asking you to sign up for it. The comparison below is still accurate on published specs; treat it as research, not a purchase. The current equivalent on llmrelay is Gemini 3.5 Flash at $0.75/M input.
Anthropic latency rating: Anthropic publishes a comparative latency rating for its own models. Google does not publish an equivalent figure, so there is nothing honest to put in the Gemini column.
Prices are llmrelay's, at 50% of official list. Specs are the vendor's own published figures (Anthropic model docs), not our benchmarks. We do not publish scores we cannot source.
Use Sonnet 5 when
- +You are already on the Anthropic API shape and want one less thing to port.
- +You need tool-use behaviour that matches the rest of a Claude-based agent stack.
- +Anthropic's Fast latency rating matters for an interactive loop.
Use Gemini 3.1 Pro when
- +You want a second opinion from a different model family on the same prompt — cheap insurance on anything consequential.
- +Your workload already leans on Google tooling and matching behaviour saves plumbing.
- +You are cost-averaging across providers so one vendor's price change cannot move your whole bill.
The honest answer
At the same price on the same key, there is no billing argument here — pick on measured output for your own prompts. Run both against fifty real inputs and count the failures; that is a cheaper experiment than a month of guessing.
What this costs you per month
At 50M input and 5M output tokens a month — a realistic heavy agent workload.
Struck-through column is the vendor's list price for the same traffic. Adjust the numbers on the calculator.
One key covers both
Switching between them is a model-id change, not a new account. Prepaid, no subscription, $10 minimum — enough to run the same prompt through both and settle the argument with your own output.
Get API key →