Gemini 3.1 Pro vs Gemini 3.5 Flash
Google's Gemini 3.1 Pro and Google's Gemini 3.5 Flash both target production language workloads, but they price and behave differently. Here is the side-by-side.
Pricing checked against provider documentation on . How we verify
The short answer
Gemini 3.5 Flash is the cheaper option — roughly 1.3x less on a blended workload, and it suits agentic loops and sub-agent fleets. Gemini 3.1 Pro justifies its premium when you need best price-to-reasoning ratio.
Google • Gemini 3.1
$2.00 / $12.00
/ 1M tokens (input / output)
Google's shipping flagship while 3.5 Pro remains unreleased, and the cheapest frontier model by a wide margin. It still tops several hard-reasoning boards including GPQA Diamond and ARC-AGI-2, making it the value choice for research-style workloads — provided you keep prompts under 200K tokens, where the price doubles.
Google • Gemini 3.5
$1.50 / $9.00
/ 1M tokens (input / output)
Google's most capable Flash model, tuned for the agentic era: sub-agent deployment, multi-step workflows, and rapid coding iterations at scale. Supports search grounding, function calling, structured outputs, and computer use in preview. Note that it is pricier than the Gemini 3 Flash preview it replaced.
Input price
Gemini 3.5 Flash is 25% cheaper than Gemini 3.1 Pro on input tokens.
Output price
Gemini 3.5 Flash is 25% cheaper than Gemini 3.1 Pro on output tokens — usually the side that dominates the bill.
Monthly cost at three workload sizes
Standard (non-batch, non-cached) rates. Reasoning models will exceed these figures because thinking tokens bill as output.
| Workload | Gemini 3.1 Pro | Gemini 3.5 Flash | Difference |
|---|---|---|---|
| Light — 1M in / 200K out | $4 | $3 | $1 |
| Moderate — 10M in / 2M out | $44 | $33 | $11 |
| Heavy — 100M in / 20M out | $440 | $330 | $110 |
Specification comparison
| Attribute | Gemini 3.1 Pro | Gemini 3.5 Flash |
|---|---|---|
| Input (/ 1M tokens) | $2.00 | $1.50 |
| Output (/ 1M tokens) | $12.00 | $9.00 |
| Cached input | — | — |
| Context window | 1,048,576 tokens | 1,048,576 tokens |
| Max output | 65,536 tokens | 65,536 tokens |
| Native reasoning | Yes | Yes |
| Knowledge cutoff | 2025-06 | 2025-01 |
| Relative latency | medium | low |
| Open weights | No | No |
| API model ID | gemini-3.1-pro-preview | gemini-3.5-flash |
| Status | preview | stable |
Gemini 3.1 Pro: Prompts over 200K tokens reprice to $4 input / $18 output per 1M.
Gemini 3.5 Flash: Flat rate at any context length, unlike Gemini 3.1 Pro's 200K cliff.
Choose Gemini 3.1 Pro if…
- Hard reasoning and research tasks
- Long-context document and video analysis
- Native multimodal pipelines
- Cost-conscious frontier workloads
Choose Gemini 3.5 Flash if…
- Sub-agent fleets and orchestration
- Fast coding iteration loops
- Search-grounded answers
- Multimodal ingestion at scale
Frequently asked
Is Gemini 3.1 Pro or Gemini 3.5 Flash cheaper?
Gemini 3.5 Flash is cheaper. On a blended 3:1 input-to-output workload it costs about 1.3x less than Gemini 3.1 Pro.
Which has the larger context window, Gemini 3.1 Pro or Gemini 3.5 Flash?
Both accept up to 1.05M tokens, so context is not a differentiator here.
Should I use Gemini 3.1 Pro or Gemini 3.5 Flash?
Pick Gemini 3.1 Pro for best price-to-reasoning ratio. Pick Gemini 3.5 Flash for agentic loops and sub-agent fleets. If cost dominates the decision, Gemini 3.5 Flash wins; if you need the capability ceiling, benchmark both on your own evals before committing.