fix(ai): price anthropic 1h cache writes at 2x input (#5738)

anthropic 1h cache writes were billed at the 5m rate; split the bucket and price the 1h portion correctly

packages/ai/src/models.ts

@@ -37,10 +37,13 @@ export function getModels<TProvider extends KnownProvider>(
 }
 
 export function calculateCost<TApi extends Api>(model: Model<TApi>, usage: Usage): Usage["cost"] {
+	// Anthropic charges 2x base input for 1h cache writes.
+	const longWrite = usage.cacheWrite1h ?? 0;
+	const shortWrite = usage.cacheWrite - longWrite;
 	usage.cost.input = (model.cost.input / 1000000) * usage.input;
 	usage.cost.output = (model.cost.output / 1000000) * usage.output;
 	usage.cost.cacheRead = (model.cost.cacheRead / 1000000) * usage.cacheRead;
-	usage.cost.cacheWrite = (model.cost.cacheWrite / 1000000) * usage.cacheWrite;
+	usage.cost.cacheWrite = (model.cost.cacheWrite * shortWrite + model.cost.input * 2 * longWrite) / 1000000;
 	usage.cost.total = usage.cost.input + usage.cost.output + usage.cost.cacheRead + usage.cost.cacheWrite;
 	return usage.cost;
 }

packages/ai/src/providers/anthropic.ts

@@ -535,6 +535,7 @@ export const streamAnthropic: StreamFunction<"anthropic-messages", AnthropicOpti
 					output.usage.output = event.message.usage.output_tokens || 0;
 					output.usage.cacheRead = event.message.usage.cache_read_input_tokens || 0;
 					output.usage.cacheWrite = event.message.usage.cache_creation_input_tokens || 0;
+					output.usage.cacheWrite1h = event.message.usage.cache_creation?.ephemeral_1h_input_tokens || 0;
 					// Anthropic doesn't provide total_tokens, compute from components
 					output.usage.totalTokens =
 						output.usage.input + output.usage.output + output.usage.cacheRead + output.usage.cacheWrite;

packages/ai/src/types.ts

@@ -267,6 +267,8 @@ export interface Usage {
 	output: number;
 	cacheRead: number;
 	cacheWrite: number;
+	/** Subset of `cacheWrite` written with 1h retention. Only Anthropic reports this split. */
+	cacheWrite1h?: number;
 	totalTokens: number;
 	cost: {
 		input: number;

packages/ai/test/anthropic-cache-write-1h-cost.test.ts

@@ -0,0 +1,86 @@
+import type Anthropic from "@anthropic-ai/sdk";
+import { describe, expect, it } from "vitest";
+import { getModel } from "../src/models.ts";
+import { streamAnthropic } from "../src/providers/anthropic.ts";
+import type { Context } from "../src/types.ts";
+
+function createSseResponse(events: Array<{ event: string; data: string }>): Response {
+	const body = events.map(({ event, data }) => `event: ${event}\ndata: ${data}\n`).join("\n");
+	return new Response(body, { status: 200, headers: { "content-type": "text/event-stream" } });
+}
+
+function createFakeAnthropicClient(response: Response): Anthropic {
+	return {
+		messages: { create: () => ({ asResponse: async () => response }) },
+	} as unknown as Anthropic;
+}
+
+function eventsWithCacheCreation(
+	cacheCreation: Record<string, number> | undefined,
+): Array<{ event: string; data: string }> {
+	const startUsage: Record<string, unknown> = {
+		input_tokens: 100,
+		output_tokens: 0,
+		cache_read_input_tokens: 0,
+		cache_creation_input_tokens: 1_000_000,
+	};
+	if (cacheCreation) startUsage.cache_creation = cacheCreation;
+	return [
+		{
+			event: "message_start",
+			data: JSON.stringify({ type: "message_start", message: { id: "msg_test", usage: startUsage } }),
+		},
+		{
+			event: "content_block_start",
+			data: JSON.stringify({ type: "content_block_start", index: 0, content_block: { type: "text", text: "" } }),
+		},
+		{
+			event: "content_block_delta",
+			data: JSON.stringify({ type: "content_block_delta", index: 0, delta: { type: "text_delta", text: "Hi" } }),
+		},
+		{ event: "content_block_stop", data: JSON.stringify({ type: "content_block_stop", index: 0 }) },
+		{
+			event: "message_delta",
+			data: JSON.stringify({
+				type: "message_delta",
+				delta: { stop_reason: "end_turn" },
+				usage: {
+					input_tokens: 100,
+					output_tokens: 5,
+					cache_read_input_tokens: 0,
+					cache_creation_input_tokens: 1_000_000,
+				},
+			}),
+		},
+		{ event: "message_stop", data: JSON.stringify({ type: "message_stop" }) },
+	];
+}
+
+// claude-opus-4-8: input 5, cacheWrite (5m) 6.25 per Mtok. 1h write = 2x input = 10.
+const context: Context = { messages: [{ role: "user", content: "hi", timestamp: Date.now() }] };
+
+describe("Anthropic 1h cache write cost", () => {
+	it("prices the 1h portion at 2x input and the rest at the 5m rate", async () => {
+		const model = getModel("anthropic", "claude-opus-4-8");
+		const response = createSseResponse(
+			eventsWithCacheCreation({ ephemeral_5m_input_tokens: 600_000, ephemeral_1h_input_tokens: 400_000 }),
+		);
+		const result = await streamAnthropic(model, context, { client: createFakeAnthropicClient(response) }).result();
+
+		expect(result.usage.cacheWrite).toBe(1_000_000);
+		expect(result.usage.cacheWrite1h).toBe(400_000);
+		// 600k * 6.25/Mtok + 400k * 10/Mtok = 3.75 + 4.0 = 7.75
+		expect(result.usage.cost.cacheWrite).toBeCloseTo(7.75, 10);
+	});
+
+	it("falls back to the 5m rate when no breakdown is reported", async () => {
+		const model = getModel("anthropic", "claude-opus-4-8");
+		const response = createSseResponse(eventsWithCacheCreation(undefined));
+		const result = await streamAnthropic(model, context, { client: createFakeAnthropicClient(response) }).result();
+
+		expect(result.usage.cacheWrite).toBe(1_000_000);
+		expect(result.usage.cacheWrite1h ?? 0).toBe(0);
+		// 1M * 6.25/Mtok = 6.25
+		expect(result.usage.cost.cacheWrite).toBeCloseTo(6.25, 10);
+	});
+});