Google Gemini pricing
Gemini 3.1 Pro Preview pricing
Gemini 3.1 Pro Preview bills per million tokens, metered separately for input and output. The current rates are below, along with the parts of the bill a per-token estimate leaves out.
Gemini 3.1 Pro Preview rates in full
All figures are USD per million tokens, taken from Google Gemini’s own pricing documentation. The API model identifier is gemini-3.1-pro-preview.
| Per million tokens | Standard, ≤200K tokens | Standard, >200K tokens |
|---|---|---|
| Input | $2 | $4 |
| Cached input read | $0.20 | $0.40 |
| Output | $12 | $18 |
What the rate table does not tell you
Google's own description: its 3rd generation Pro model, built for multimodal understanding, agentic capabilities, and vibe-coding.
Requests over 200K input tokens bill at double the input rate and 50% more on output, the same context-based pricing split OpenAI and xAI use on their own frontier models.
Context caching storage is billed separately at $4.50 per million tokens per hour, on top of the discounted cached-read rate shown here.
A worked monthly example
Take 500,000 calls in a month at 3,000 input tokens and 400 output tokens each. That is 1.5 billion input tokens against 200 million output tokens, so input is 88% of the token volume.
| Line | Tokens | Rate | Cost |
|---|---|---|---|
| Input | 1,500M | $2 | $3,000 |
| Output | 200M | $12 | $2,400 |
| Total | 1,700M | $5,400 |
Output is 12% of the tokens and 44% of the bill. That inversion is why prompt trimming so often fails to move the invoice, and it is the single most common reason a forecast built on Gemini 3.1 Pro Preview comes in under the real number.
How this page stays current
Most third-party pricing tables are typed in once and quietly rot. This one is generated from a checked figure with the date and source recorded, and it is cross-checked on every deploy against the live model catalog Spendline uses to price real API traffic. If the two disagree, the site fails to build rather than publishing a stale number. At the last build the catalog agreed: $2 input and $12 output.
Frequently asked questions
How much does the Gemini 3.1 Pro Preview API cost?
Gemini 3.1 Pro Preview is billed per million tokens, metered separately for input and output. As of September 16, 2026 the rate is $2 per million input tokens and $12 per million output tokens, with cached input read at $0.20.
Why is my Gemini 3.1 Pro Preview bill higher than the per-token estimate?
Most estimates multiply expected tokens by the input rate and stop there. Output is priced at $12 against $2 for input, so responses usually dominate the bill even when prompts look larger. Reasoning tokens bill as output. Retries and agent fan-out pay full input cost for calls that produced nothing. And a cache that gets written but never read is pure overhead rather than a saving.
What is the cheapest way to run Gemini 3.1 Pro Preview?
Caching a stable prefix takes repeat input to $0.20, 10% of the standard rate, and pays for itself once the cached content is read more often than it is written. The larger lever is usually routing: sending the requests that do not need this tier to a cheaper model, and capping spend per customer before the call goes out.
How do I track Gemini 3.1 Pro Preview spend per customer or per feature?
The provider invoice is one number for the whole organization, so per-customer cost has to be attributed at the call. That means tagging every request with the customer, team, or agent it belongs to and recording the resolved cost against that tag in a ledger you can close monthly. Spendline does this by sitting in front of the API, which also lets a budget be enforced before the request is forwarded rather than reported after.
Know what this costs per customer, not just per token
A rate card tells you what a token costs. It does not tell you which customer, team, or agent spent it, or stop the one that is running away. Spendline sits in front of the API so every call is attributed and checked against a budget before it is forwarded.
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