packages/ai/src/utils/cost.ts

// Adapted from Pi cd34e17ff039502f3664d8363b3c0a23f93a2ca3.
// Copyright (c) 2025 Mario Zechner. MIT: licenses/third-party-notices.txt.
import type { Api, Model, Usage } from "../types.ts";

export function calculateCost<TApi extends Api>(model: Model<TApi>, usage: Usage): Usage["cost"] {
  const inputTokens = usage.input + usage.cacheRead + usage.cacheWrite;
  let rates: Model["cost"] = model.cost;
  let matchedThreshold = -1;
  for (const tier of model.cost.tiers ?? []) {
    if (inputTokens > tier.inputTokensAbove && tier.inputTokensAbove > matchedThreshold) {
      rates = tier;
      matchedThreshold = tier.inputTokensAbove;
    }
  }

  // Anthropic charges 2x base input for 1h cache writes.
  const longWrite = usage.cacheWrite1h ?? 0;
  const shortWrite = usage.cacheWrite - longWrite;
  usage.cost.input = (rates.input / 1000000) * usage.input;
  usage.cost.output = (rates.output / 1000000) * usage.output;
  usage.cost.cacheRead = (rates.cacheRead / 1000000) * usage.cacheRead;
  usage.cost.cacheWrite = (rates.cacheWrite * shortWrite + rates.input * 2 * longWrite) / 1000000;
  usage.cost.total = usage.cost.input + usage.cost.output + usage.cost.cacheRead + usage.cost.cacheWrite;
  return usage.cost;
}