Choosing between Gemini 3.5 Flash (Google) and GPT-5.5 (OpenAI)? This is a side-by-side of their API pricing, context windows, and real cost on a sample workload — so you can pick on the numbers, not the marketing.
Gemini 3.5 Flash vs GPT-5.5: pricing & specs
| Gemini 3.5 Flash | GPT-5.5 | |
|---|---|---|
| Vendor | OpenAI | |
| Input / 1M tokens | $1.50 | $5.00 |
| Output / 1M tokens | $9.00 | $30.00 |
| Cached input / 1M | — | $0.50 |
| Context window | 1M tokens | 400K tokens |
Cost example: 1M input + 1M output tokens
For a workload of 1M input plus 1M output tokens, Gemini 3.5 Flash costs $10.50 and GPT-5.5 costs $35.00 — Gemini 3.5 Flash is about 70% cheaper on this mix. Your real ratio of input to output tokens shifts the math; plug in your own numbers with the token cost calculator.
Which should you choose?
- Lower cost: Gemini 3.5 Flash is cheaper on output tokens ($9.00 vs $30.00 / 1M), which usually dominates spend on generation-heavy workloads.
- Larger context window: Gemini 3.5 Flash fits more in one prompt (1M tokens) — better for long documents or big RAG context.
- Ecosystem: pick the provider whose SDK, rate limits, and tooling fit your stack — see Google rate limits and OpenAI rate limits.
Full specs: Gemini 3.5 Flash · GPT-5.5. Thinking of switching providers? See the migration guides.
Prices as of June 2026 and change often — verify before relying on them.