LLM Cost Calculator — Kotlin source

// llm-cost-calculator — Kotlin port: per-million-token cost math for LLM workloads.

/** Multiplier applied to Batch API pricing (the standard 50% discount). */
const val BATCH_DISCOUNT = 0.5

/** Price pair for a model or a custom rate card. null = unpriced. */
data class CostRates(val inputPerM: Double?, val outputPerM: Double?)

/** One workload to price. */
data class CostInput(
    val inputTokens: Long,
    val outputTokens: Long,
    val requests: Long = 1,
    val batch: Boolean = false,
)

/** Pricing projection of a model — the only three fields cost math needs. */
data class Model(val id: String, val inputPerM: Double?, val outputPerM: Double?)

/** Cost in USD, or null when either rate is unpriced:
 * ((in/1e6)·input + (out/1e6)·output) × requests × batch discount. */
fun costFor(rates: CostRates, work: CostInput): Double? {
    val input = rates.inputPerM ?: return null
    val output = rates.outputPerM ?: return null
    val base = work.inputTokens / 1e6 * input + work.outputTokens / 1e6 * output
    return base * work.requests * if (work.batch) BATCH_DISCOUNT else 1.0
}

/** Output tokens per USD: 1e6 / outputPerM, or null when unpriced. */
fun tokensPerDollar(m: Model): Double? = m.outputPerM?.let { 1e6 / it }

fun main() {
    val models = listOf(
        Model("sonnet-class", 3.0, 15.0),
        Model("budget-class", 0.5, 2.0),
        Model("preview", null, null), // unpriced model
    )
    val work = CostInput(inputTokens = 12_000, outputTokens = 3_000, requests = 250, batch = true)

    // Cheapest first, unpriced last, ties by id — the TS comparator as a sort key.
    models.sortedWith(
        compareBy(
            { costFor(CostRates(it.inputPerM, it.outputPerM), work) == null },
            { costFor(CostRates(it.inputPerM, it.outputPerM), work) ?: 0.0 },
            { it.id },
        )
    ).forEach { m ->
        val cost = costFor(CostRates(m.inputPerM, m.outputPerM), work)
        println(
            if (cost != null) "%-14s $%.4f  (%,.0f output tokens/USD)".format(m.id, cost, tokensPerDollar(m) ?: 0.0)
            else "%-14s unpriced".format(m.id)
        )
    }
}