Gemini 3.1 Pro vs Gemini 3.5 Flash: which API costs less?
Averaged across three realistic workloads, Gemini 3.5 Flash is about 25% cheaper than Gemini 3.1 Pro. Below: raw rates and side-by-side monthly costs, computed from prices verified 2026-07-05 (we track what you are billed today, promos included).
Rates per 1M tokens
| Model | Input | Output | Cached input |
|---|---|---|---|
| Gemini 3.1 ProGoogle | $2 | $12 | — |
| Gemini 3.5 FlashGoogle | $1.50 | $9 | — |
Gemini 3.1 Pro: Do 200K tokenow promptu; powyzej 2x cena.
Monthly cost, side by side
| Workload | Gemini 3.1 Pro | Gemini 3.5 Flash | Difference |
|---|---|---|---|
Customer-support chatbot 2M input + 0.5M output tokens/month, 60% of input served from prompt cache | $10.00 | $7.50 | Gemini 3.5 Flash −25% |
RAG / document Q&A 20M input + 1M output tokens/month, 70% cached (shared context) | $52.00 | $39.00 | Gemini 3.5 Flash −25% |
Agentic coding assistant 50M input + 5M output tokens/month, 80% cached (long sessions) | $160 | $120 | Gemini 3.5 Flash −25% |
Your traffic looks different? Run your own numbers in the calculator.
FAQ
Which is cheaper: Gemini 3.1 Pro or Gemini 3.5 Flash?
Across three realistic workloads (chatbot, RAG, agent), Gemini 3.5 Flash works out about 25% cheaper than Gemini 3.1 Pro on average. Raw rates: Gemini 3.1 Pro $2/$12 per 1M tokens vs Gemini 3.5 Flash $1.50/$9. Verified 2026-07-05.
Does prompt caching change the comparison?
Yes — cached input costs the full input rate on Gemini 3.1 Pro (no cache discount listed) and the full input rate on Gemini 3.5 Flash (no cache discount listed). Our scenario numbers already include realistic cache hit rates.
Is cheaper always better?
No. Price is one axis — model capability, context window and latency differ. This page answers only the cost question; benchmark quality on your own tasks before switching.