# Gemini 3.8 Flash vs GPT-5.5

> Markdown mirror of https://router.one/models/compare/gemini-3-8-flash-vs-gpt-5-5 for AI assistants and crawlers. Router One is an OpenAI-compatible LLM API gateway.

Gemini 3.8 Flash is the lower-priced of the two on Router One — about 51% less on a 1M-input + 1M-output mix. Both carry a 1.05M context window. Gemini 3.8 Flash answers on /v1/chat/completions; GPT-5.5 on /v1/chat/completions and /v1/responses (Codex CLI).

Gemini 3.8 Flash and GPT-5.5 compared on current per-token rates, context window, and capabilities — both callable through one OpenAI-compatible endpoint with per-request cost traces.

## Gemini 3.8 Flash vs GPT-5.5: rates, context window, and capabilities

| Spec | Gemini 3.8 Flash | GPT-5.5 |
| --- | --- | --- |
| Input / 1M tokens | $0.225 | $0.50 |
| Output / 1M tokens | $1.125 | $2.25 |
| Cached input / 1M tokens | $0.225 | $0.125 |
| Context window | 1.05M | 1.05M |
| Detail page | [Gemini 3.8 Flash](https://router.one/models/gemini-3-8-flash) | [GPT-5.5](https://router.one/models/gpt-5-5) |

## What does 1M tokens cost on Gemini 3.8 Flash vs GPT-5.5?

For a workload of 1M input plus 1M output tokens at current rates: Gemini 3.8 Flash comes to $1.35, GPT-5.5 comes to $2.75 — Gemini 3.8 Flash is about 51% cheaper on this mix. Real workloads skew heavily toward input tokens, so weigh the input rate by your own ratio; the cached-input row above is the posted catalog rate for that model.

## Switch between Gemini 3.8 Flash and GPT-5.5 without changing code

Both models are behind the same OpenAI-compatible endpoint, so an A/B test is a one-string change — same key, same code, and every request traced with tokens, cost, and latency in the dashboard:

`compare.sh`

```bash
curl https://api.router.one/v1/chat/completions \
  -H "Authorization: Bearer sk-your-router-one-key" \
  -H "Content-Type: application/json" \
  -d '{"model": "google/gemini-3.8-flash", "messages": [{"role": "user", "content": "Hello"}]}'

# Same request, other model — change one string:
#   "model": "openai/gpt-5.5"
```

## FAQ

### Is Gemini 3.8 Flash cheaper than GPT-5.5?

Input: Gemini 3.8 Flash $0.225 vs GPT-5.5 $0.50 / 1M tokens; Gemini 3.8 Flash has the lower rate. Output: Gemini 3.8 Flash $1.125 vs GPT-5.5 $2.25 / 1M tokens; Gemini 3.8 Flash has the lower rate. Total cost depends on the workload's input, output and cache usage. Rates change; the /models page is the live source of truth.

### Can I switch between Gemini 3.8 Flash and GPT-5.5 without changing code?

Yes. Both are served through the same OpenAI-compatible endpoint, so switching is changing the model string in the request — the key, base URL, and request shape stay identical.

### Where do these numbers come from?

Specs and prices on this page render from the live Router One catalog — the same data as the /models page — and refresh with it. Pricing methodology is documented on /pricing-methodology. Rates on this page were read from the live catalog on 2026-09-20 (UTC) and refresh within the hour.

## More comparisons

- [GPT-5.5 vs Claude Sonnet 5](https://router.one/models/compare/gpt-5-5-vs-claude-sonnet-5)
- [Claude Opus 4.8 vs GPT-5.5](https://router.one/models/compare/claude-opus-4-8-vs-gpt-5-5)
- [DeepSeek V4.1 Flash vs Gemini 3.8 Flash](https://router.one/models/compare/deepseek-v4-1-flash-vs-gemini-3-8-flash)
- [DeepSeek V4.1 Flash vs GPT-5.5](https://router.one/models/compare/deepseek-v4-1-flash-vs-gpt-5-5)

## See also

- Canonical page: https://router.one/models/compare/gemini-3-8-flash-vs-gpt-5-5
- All model comparisons: https://router.one/models/compare
- All models & prices: https://router.one/models (markdown: https://router.one/models.md)
- Pricing: https://router.one/pricing
- Gemini API in China: https://router.one/gemini-api-china
- GPT API access: https://router.one/cheap-gpt-api
- Cost calculator: https://router.one/llm-cost-calculator
- Pricing methodology: https://router.one/pricing-methodology