cost.rs

crates/cortex-core/src/cost.rs

1. //! Money. Stored as whole nano-dollars (1e-9 USD) in an i64, so sums over a
2. //! month never drift the way floats do. A message keeps the prices it was
3. //! billed at, so a later price change never rewrites history.
5. use crate::types::{Prices, Usage};
7. pub const NANO_PER_USD: f64 = 1e9;
9. /// Cost of one completion. Cached prompt tokens bill at the cache-read price
10. /// when the model has one, otherwise at the input price.
11. pub fn cost_nanousd(usage: &Usage, prices: &Prices) -> i64 {
12. let cached = usage.cached_tokens.clamp(0, usage.prompt_tokens.max(0));
13. let uncached = (usage.prompt_tokens - cached).max(0);
14. let cache_price = prices.cache_read_per_m.unwrap_or(prices.input_per_m);
15. // $/1M tokens * tokens / 1e6 * 1e9 nano = price * tokens * 1000
16. let nano = uncached as f64 * prices.input_per_m * 1000.0
17. + cached as f64 * cache_price * 1000.0
18. + usage.completion_tokens.max(0) as f64 * prices.output_per_m * 1000.0;
19. nano.round() as i64
20. }
22. pub fn to_usd(nano: i64) -> f64 {
23. nano as f64 / NANO_PER_USD
24. }
26. /// "$0.0012", "$1.24", "<$0.0001", "$0".
27. pub fn format_usd(nano: i64) -> String {
28. if nano == 0 {
29. return "$0".into();
30. }
31. let usd = to_usd(nano);
32. if usd < 0.0001 {
33. "<$0.0001".into()
34. } else if usd < 1.0 {
35. format!("${usd:.4}")
36. } else {
37. format!("${usd:.2}")
38. }
39. }
41. #[cfg(test)]
42. mod tests {
43. use super::*;
45. const P: Prices = Prices { input_per_m: 0.5, output_per_m: 1.5, cache_read_per_m: Some(0.1) };
47. #[test]
48. fn hand_calculated() {
49. // 1,000 in at $0.50/M = $0.0005; 2,000 out at $1.50/M = $0.003. Total $0.0035.
50. let u = Usage { prompt_tokens: 1000, completion_tokens: 2000, cached_tokens: 0 };
51. assert_eq!(cost_nanousd(&u, &P), 3_500_000);
52. assert_eq!(format_usd(3_500_000), "$0.0035");
53. }
55. #[test]
56. fn cached_tokens_bill_at_cache_price() {
57. // 600 uncached * 0.5 + 400 cached * 0.1 = 300,000 + 40,000 nano (x1000 scale)
58. let u = Usage { prompt_tokens: 1000, completion_tokens: 0, cached_tokens: 400 };
59. assert_eq!(cost_nanousd(&u, &P), 340_000);
60. let no_cache_price = Prices { cache_read_per_m: None, ..P };
61. assert_eq!(cost_nanousd(&u, &no_cache_price), 500_000);
62. }
64. #[test]
65. fn odd_inputs_are_safe() {
66. let u = Usage { prompt_tokens: 10, completion_tokens: -5, cached_tokens: 99 };
67. assert_eq!(cost_nanousd(&u, &P), 1_000); // cached clamps to 10, negatives to 0
68. assert_eq!(cost_nanousd(&Usage::default(), &Prices::default()), 0);
69. }
71. #[test]
72. fn formatting() {
73. assert_eq!(format_usd(0), "$0");
74. assert_eq!(format_usd(12), "<$0.0001");
75. assert_eq!(format_usd(1_240_000_000), "$1.24");
76. assert_eq!(format_usd(120_000), "$0.0001");
77. }
78. }