Head-to-head
Gemini 3.1 Pro Preview vs Gemini 3.5 Flash
Compare Gemini 3.1 Pro Preview and Gemini 3.5 Flash on the metrics that decide an agent workload.
| Metric | Gemini 3.1 Pro Preview | Gemini 3.5 Flash |
|---|---|---|
| Provider | Google Gemini | Google Gemini |
| Input / 1M | $2.00 | $1.50 |
| Output / 1M | $12.00 | $9.00 |
| Cache read / 1M | $0.20 (−90%) | $0.15 (−90%) |
| Reuse-adj @55% | $3.76 | $2.82 |
| Context | 1M | 1M |
| Cache capture | 83% | 86% |
| Warm TTFT | 360ms (−56%) | 150ms (−61%) |
| Quality index | 93 | 96 |
Teal marks the better value in each row. Reuse-adjusted assumes 55% prefix reuse and a 25% output share.
Pick Gemini 3.1 Pro Preview when your stack already standardizes on it.
Pick Gemini 3.5 Flash when it scores higher on the composite quality index, it is cheaper once prefix reuse is priced in, it answers faster on warm cache hits.
Gemini 3.5 Flash wins on both reuse-adjusted cost and quality here, so it is the default pick. Reach for Gemini 3.1 Pro Preview only when a specific constraint (modality, latency floor, or licensing) forces it.
Frequently asked
Gemini 3.1 Pro Preview vs Gemini 3.5 Flash, answered.
Is Gemini 3.1 Pro Preview or Gemini 3.5 Flash cheaper?
At 55% prefix reuse, Gemini 3.1 Pro Preview blends to about $3.76 per 1M tokens and Gemini 3.5 Flash to about $2.82. Gemini 3.5 Flash is cheaper on that basis.
Which has the larger context window?
Gemini 3.1 Pro Preview has the larger window: 1M vs 1M tokens.
Which captures more reuse?
Gemini 3.5 Flash shows higher measured cache capture (86% vs 83%) in the Zumik corpus.
Let an alias pick for you.
Route to whichever model wins under current policy automatically. Zumik resolves the alias to the best fit per request, so you never hard-code a loser.