Crate gemini_cost 

gemini-cost

Calculate Google Gemini API call cost from a usage block.

Gemini’s usageMetadata block reports promptTokenCount, candidatesTokenCount, and cachedContentTokenCount. Some models charge a different rate when promptTokenCount > 200_000. This crate gives you a small Pricing table for popular Gemini models plus a Usage struct that knows how to compute cost from those fields.

Pricing is best-effort and dated; verify against https://ai.google.dev/gemini-api/docs/pricing before using these numbers for billing.

Quick example

use gemini_cost::{Usage, default_pricing};

let pricing = default_pricing("gemini-2.5-pro").unwrap();
let usage = Usage {
    input_tokens: 1_000,
    output_tokens: 500,
    cached_input_tokens: 0,
};
let cost = pricing.cost_for(&usage);
assert!(cost > 0.0);

Long-prompt tiers

Gemini 2.5 Pro switches to a higher rate when input_tokens exceeds 200,000. The pricing table carries both tiers; cost_for picks the right one automatically.

use gemini_cost::{Pricing, Usage, default_pricing};
let p = default_pricing("gemini-2.5-pro").unwrap();
let short = p.cost_for(&Usage { input_tokens: 100_000, output_tokens: 0, cached_input_tokens: 0 });
let long  = p.cost_for(&Usage { input_tokens: 300_000, output_tokens: 0, cached_input_tokens: 0 });
assert!(long > short * 3.0); // long-tier is more than the 3x scale alone

BYO pricing

use gemini_cost::{Pricing, Usage};
let custom = Pricing::flat(0.5, 2.0, 0.05);
let _ = custom.cost_for(&Usage::default());

Structs

Pricing

Per-model rates, USD per 1M tokens.

Usage

Three-field token usage as returned by Gemini’s usageMetadata.

Constants

DEFAULT_PRICING_TABLE

Built-in pricing table. Source: ai.google.dev/gemini-api/docs/pricing as of 2026-Q2. VERIFY before billing.

LONG_PROMPT_THRESHOLD

Models above this fresh-input-token count are billed at the long-prompt tier.

Functions

default_pricing

Look up the price table entry for a Gemini model id.

normalize_model_id

Strip a Vertex resource-path prefix and any trailing -(preview|exp)-MM-DD snapshot suffix.