Model comparison
Gemini 3.5 Flash vs Grok 4.20 Reasoning
Compare Gemini 3.5 Flash vs Grok 4.20 Reasoning API pricing: input/output token costs, cache pricing, context windows, workload estimates, and routing fit.
Gemini 3.5 Flash
gemini · gemini-3.5-flash
- Input
- $1.5
- Output
- $9
- Context
- 1M
Grok 4.20 Reasoning
xai · grok-4.20-0309-reasoning
- Input
- $1.25
- Output
- $2.5
- Context
- 1M
Quick take
Grok 4.20 Reasoning has the lower input price at $1.25 per 1M input tokens. Grok 4.20 Reasoning is cheaper for the example blended workload below. Gemini 3.5 Flash has the larger context window at 1M tokens.
Choose Gemini 3.5 Flash if...
- Gemini 3.5 Flash is safer for long documents, repository analysis, and RAG prompts because it has the larger context window.
- Gemini 3.5 Flash gives more room for long generated answers, reports, or code output.
- Gemini 3.5 Flash is required if images, screenshots, or visual documents are part of the workflow.
Choose Grok 4.20 Reasoning if...
- Grok 4.20 Reasoning is the better default for cost-sensitive traffic and repeated high-volume calls.
Example workload cost
Estimates use input tokens plus 20% output tokens. They exclude provider discounts, cache hits, and tool/search surcharges.
| Workload | Gemini 3.5 Flash | Grok 4.20 Reasoning | Cheaper |
|---|---|---|---|
| 1M input + 200K output | $3.30 | $1.75 | Grok 4.20 Reasoning |
| 10M input + 2M output | $33.00 | $17.50 | Grok 4.20 Reasoning |
| 100M input + 20M output | $330.00 | $175.00 | Grok 4.20 Reasoning |
Context, output, and capability fit
Gemini 3.5 Flash provides the larger context window. Check max output separately when the task needs long reports, code generation, or full-document rewrites.
- Gemini 3.5 Flash max output
- 65.5K
- Grok 4.20 Reasoning max output
- n/a
- Gemini 3.5 Flash features
- prompt caching, function calling, vision
- Grok 4.20 Reasoning features
- prompt caching, function calling
Risk notes for Gemini 3.5 Flash
- No major capability risk is flagged in this snapshot, but provider pages should still be verified before production routing.
Risk notes for Grok 4.20 Reasoning
- No major capability risk is flagged in this snapshot, but provider pages should still be verified before production routing.
Routing tags
fastreasoninglong-contextmultimodalcache-friendlystablebudgetragfrontieragents