Gemini 3.5 Flash vs Gemini 3.1 Pro Preview Custom Tools
API pricing, benchmark indices and specs — updated 19 October 2026.
google · A · API-only
Input / 1M
$1.50
Output / 1M
$9.00
AA index
33.6
proprietary · 1M context
google · B · API-only
Input / 1M
$2.00
Output / 1M
$12.00
AA index
—
proprietary · 1M context
Specification comparison
Differences are highlighted; identical values are muted.
| Specification | Gemini 3.5 Flash | Gemini 3.1 Pro Preview Custom Tools |
|---|---|---|
| Deployment | API-only (closed weights) | API-only (closed weights) |
| Parameters | n/a — API-only | n/a — API-only |
| Architecture | n/a — API-only | n/a — API-only |
| Context length | 1,048,576 | 1,048,576 |
| Licence | Proprietary | Proprietary |
| Commercial use | Per API terms | Per API terms |
| Languages | n/a — API-only | n/a — API-only |
| Downloads 30d | n/a — API-only | n/a — API-only |
| Downloads all time | n/a — API-only | n/a — API-only |
| Quantizations on the Hub | n/a — API-only | n/a — API-only |
| Gated | n/a — API-only | n/a — API-only |
| First seen on the Hub | n/a — API-only | n/a — API-only |
| API input price / 1M tokens | $1.50 | $2.00 |
| API output price / 1M tokens | $9.00 | $12.00 |
| Est. cost per 1M input + 1M output tokens | $10.50 | $14.00 |
| Cached input / 1M tokens | $0.15 | $0.20 |
| AA Intelligence Index | 33.6 | — |
| AA Coding Index | — | — |
| AA Agentic Index | — | — |
| Max output tokens | 65,536 | 65,536 |
| API providers | 2 | 1 |
| Tool calling | Yes | Yes |
| Reasoning mode | Yes | Yes |
API cost
Estimated cost of 1M input + 1M output tokens via OpenRouter
Gemini 3.5 Flash
$10.50
Gemini 3.1 Pro Preview Custom Tools
$14.00
Gemini 3.5 Flash is 1.3× cheaper at list price.