GPT-5.5 vs Gemini 3.1 Pro: which API costs less?
Averaged across three realistic workloads, Gemini 3.1 Pro is about 60% cheaper than GPT-5.5. Below: raw rates and side-by-side monthly costs, computed from prices verified 2026-10-17 (we track what you are billed today, promos included).
Rates per 1M tokens
| Model | Input | Output | Cached input |
|---|---|---|---|
| GPT-5.5OpenAI | $5 | $30 | $0.500 |
| Gemini 3.1 ProGoogle | $2 | $12 | $0.200 |
GPT-5.5: Prompts up to 272K tokens; longer prompts cost more. Gemini 3.1 Pro: Preview; prompts up to 200K tokens; longer prompts cost $4/$18.
Monthly cost, side by side
| Workload | GPT-5.5 | Gemini 3.1 Pro | Difference |
|---|---|---|---|
Customer-support chatbot 2M input + 0.5M output tokens/month, 60% of input served from prompt cache | $19.60 | $7.84 | Gemini 3.1 Pro −60% |
RAG / document Q&A 20M input + 1M output tokens/month, 70% cached (shared context) | $67.00 | $26.80 | Gemini 3.1 Pro −60% |
Agentic coding assistant 50M input + 5M output tokens/month, 80% cached (long sessions) | $220 | $88.00 | Gemini 3.1 Pro −60% |
Your traffic looks different? Run your own numbers in the calculator.
FAQ
Which is cheaper: GPT-5.5 or Gemini 3.1 Pro?
Across three realistic workloads (chatbot, RAG, agent), Gemini 3.1 Pro works out about 60% cheaper than GPT-5.5 on average. Raw rates: GPT-5.5 $5/$30 per 1M tokens vs Gemini 3.1 Pro $2/$12. Verified 2026-10-17.
Does prompt caching change the comparison?
Yes — cached input costs $0.500 on GPT-5.5 and $0.200 on Gemini 3.1 Pro. 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.