# Gemini 4 Hydrogen vs Gemini 3.8 Flash

> Markdown mirror of https://router.one/models/compare/gemini-4-hydrogen-vs-gemini-3-8-flash for AI assistants and crawlers. Router One is a unified, OpenAI-compatible LLM API gateway.

Gemini 3.8 Flash is the lower-priced of the two on Router One — about 50% less on a 1M-input + 1M-output mix. Both carry a 1.05M context window. Both answer on /v1/chat/completions. Gemini 4 Hydrogen is in no plan and bills the wallet; Gemini 3.8 Flash counts against the Standard models allowance on Pro, Max and Ultra.

Gemini 4 Hydrogen and Gemini 3.8 Flash compared on current per-token rates, context window, and capabilities — both callable through one OpenAI-compatible endpoint that logs each request it forwards.

## Gemini 4 Hydrogen vs Gemini 3.8 Flash: rates, context window, and capabilities

| Spec | Gemini 4 Hydrogen | Gemini 3.8 Flash |
| --- | --- | --- |
| Input / 1M tokens | $0.45 | $0.225 |
| Output / 1M tokens | $2.25 | $1.125 |
| Cached input / 1M tokens | $0.0225 | $0.0225 |
| Context window | 1.05M | 1.05M |
| Capabilities | Chat, Streaming, Tool calling, Vision | Chat, Streaming, Tool calling, Vision |
| Subscription plans | Not in any plan — wallet | Standard models — Pro, Max, Ultra |
| Detail page | [Gemini 4 Hydrogen](https://router.one/models/gemini-4-hydrogen) | [Gemini 3.8 Flash](https://router.one/models/gemini-3-8-flash) |

## What does 1M tokens cost on Gemini 4 Hydrogen vs Gemini 3.8 Flash?

For a workload of 1M input plus 1M output tokens at current rates: Gemini 4 Hydrogen comes to $2.70, Gemini 3.8 Flash comes to $1.35 — Gemini 3.8 Flash is about 50% 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 4 Hydrogen and Gemini 3.8 Flash

The API key, base URL, endpoint and request shape stay the same — Router One serves both on /v1/chat/completions, so on the wire the switch is a model-string change. Per Google's What's new in Gemini 4 Hydrogen page (checked 2026-11-13), Google calls Gemini 4 Hydrogen its recommended upgrade from Gemini 3.8 Flash, and its migration checklist lists these changes on Google's own Gemini API: Gemini 3.8 Flash keeps separate input and output budgets, while Gemini 4 Hydrogen shares one window across input, thinking and output, so Google says to remove hard-coded low output caps or raise them to 65,536; Gemini 4 Hydrogen defaults to the high thinking level rather than medium, adds xhigh and rejects a minimal thinking level with an error; it does not support explicit context caching; and Google says to remove temperature, top_p and top_k. On a Pro, Max or Ultra plan the billing differs: as of the 2026-11-13 plan response, Gemini 4 Hydrogen is in no plan tier and bills the wallet per token; Gemini 3.8 Flash counts against the Standard models allowance. Test the parameters your code sends on your own prompts before you move a workload.

`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-4-hydrogen", "messages": [{"role": "user", "content": "Hello"}]}'

# Same request, other model — change one string:
#   "model": "google/gemini-3.8-flash"
```

## FAQ

### Is Gemini 4 Hydrogen cheaper than Gemini 3.8 Flash?

Input: Gemini 4 Hydrogen $0.45 vs Gemini 3.8 Flash $0.225 / 1M tokens; Gemini 3.8 Flash has the lower rate. Output: Gemini 4 Hydrogen $2.25 vs Gemini 3.8 Flash $1.125 / 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.

### Is Gemini 4 Hydrogen or Gemini 3.8 Flash included in a Router One subscription?

Gemini 4 Hydrogen is in no Router One plan, so every call bills the wallet per token. Gemini 3.8 Flash counts against the Standard models allowance on Pro, Max and Ultra: Pro 5,000, Max 8,000 and Ultra 25,000 requests per 30-day cycle, shared by every model in that tier. Gemini 3.8 Flash requests above its long-context threshold count as more than one quota request. Requests beyond a plan's allowance bill the wallet per token.

### Can I switch between Gemini 4 Hydrogen and Gemini 3.8 Flash without changing code?

The API key, base URL, endpoint and request shape stay the same — Router One serves both on /v1/chat/completions, so on the wire the switch is a model-string change. Per Google's What's new in Gemini 4 Hydrogen page (checked 2026-11-13), Google calls Gemini 4 Hydrogen its recommended upgrade from Gemini 3.8 Flash, and its migration checklist lists these changes on Google's own Gemini API: Gemini 3.8 Flash keeps separate input and output budgets, while Gemini 4 Hydrogen shares one window across input, thinking and output, so Google says to remove hard-coded low output caps or raise them to 65,536; Gemini 4 Hydrogen defaults to the high thinking level rather than medium, adds xhigh and rejects a minimal thinking level with an error; it does not support explicit context caching; and Google says to remove temperature, top_p and top_k. On a Pro, Max or Ultra plan the billing differs: as of the 2026-11-13 plan response, Gemini 4 Hydrogen is in no plan tier and bills the wallet per token; Gemini 3.8 Flash counts against the Standard models allowance. Test the parameters your code sends on your own prompts before you move a workload.

### 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 2026-11-13 (UTC) and refresh within the hour.

## More comparisons

- [Gemini 3.8 Flash vs GPT-5.6 Terra](https://router.one/models/compare/gemini-3-8-flash-vs-gpt-5-6-terra)
- [Gemini 3.8 Flash vs Gemini 3.7 Flash](https://router.one/models/compare/gemini-3-8-flash-vs-gemini-3-7-flash)
- [Gemini 4 Hydrogen vs Gemini 4 Carbon](https://router.one/models/compare/gemini-4-hydrogen-vs-gemini-4-carbon)
- [DeepSeek V4.1 Flash vs Gemini 3.8 Flash](https://router.one/models/compare/deepseek-v4-1-flash-vs-gemini-3-8-flash)

## See also

- Canonical page: https://router.one/models/compare/gemini-4-hydrogen-vs-gemini-3-8-flash
- 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
- Gemini 4 Hydrogen API guide: https://router.one/blog/gemini-4-hydrogen-api-guide
- Gemini 3.8 Flash API guide: https://router.one/blog/gemini-3-8-flash-api-guide
- Cost calculator: https://router.one/llm-cost-calculator
- Pricing methodology: https://router.one/pricing-methodology