feat(ai): Add cost tracking to LLM implementations

- Track input/output token costs for all providers
- Calculate costs based on Model pricing information
- Include cost information in AssistantMessage responses
- Add Usage interface with detailed cost breakdown
- Implement calculateCost utility function for cost calculations

packages/ai/src/models.ts

@@ -3,7 +3,7 @@ import { AnthropicLLM } from "./providers/anthropic.js";
 import { GoogleLLM } from "./providers/google.js";
 import { OpenAICompletionsLLM } from "./providers/openai-completions.js";
 import { OpenAIResponsesLLM } from "./providers/openai-responses.js";
-import type { Model } from "./types.js";
+import type { Model, Usage } from "./types.js";
 
 // Provider configuration with factory functions
 export const PROVIDER_CONFIG = {
@@ -102,5 +102,14 @@ export function getModel<P extends keyof typeof PROVIDERS>(
 	return models[modelId as string];
 }
 
+export function calculateCost(model: Model, usage: Usage) {
+	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.total = usage.cost.input + usage.cost.output + usage.cost.cacheRead + usage.cost.cacheWrite;
+	return usage.cost;
+}
+
 // Re-export Model type for convenience
 export type { Model };

packages/ai/src/providers/anthropic.ts

@@ -5,6 +5,7 @@ import type {
 	MessageParam,
 	Tool,
 } from "@anthropic-ai/sdk/resources/messages.js";
+import { calculateCost } from "../models.js";
 import type {
 	AssistantMessage,
 	Context,
@@ -13,8 +14,8 @@ import type {
 	Message,
 	Model,
 	StopReason,
-	TokenUsage,
 	ToolCall,
+	Usage,
 } from "../types.js";
 
 export interface AnthropicLLMOptions extends LLMOptions {
@@ -186,13 +187,20 @@ export class AnthropicLLM implements LLM<AnthropicLLMOptions> {
 					name: block.name,
 					arguments: block.input as Record<string, any>,
 				}));
-			const usage: TokenUsage = {
+			const usage: Usage = {
 				input: msg.usage.input_tokens,
 				output: msg.usage.output_tokens,
 				cacheRead: msg.usage.cache_read_input_tokens || 0,
 				cacheWrite: msg.usage.cache_creation_input_tokens || 0,
-				// TODO add cost
+				cost: {
+					input: 0,
+					output: 0,
+					cacheRead: 0,
+					cacheWrite: 0,
+					total: 0,
+				},
 			};
+			calculateCost(this.modelInfo, usage);
 
 			return {
 				role: "assistant",
@@ -215,6 +223,7 @@ export class AnthropicLLM implements LLM<AnthropicLLMOptions> {
 					output: 0,
 					cacheRead: 0,
 					cacheWrite: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 				},
 				stopReason: "error",
 				error: error instanceof Error ? error.message : String(error),

packages/ai/src/providers/google.ts

@@ -5,6 +5,7 @@ import {
 	type GenerateContentParameters,
 	GoogleGenAI,
 } from "@google/genai";
+import { calculateCost } from "../models.js";
 import type {
 	AssistantMessage,
 	Context,
@@ -13,9 +14,9 @@ import type {
 	Message,
 	Model,
 	StopReason,
-	TokenUsage,
 	Tool,
 	ToolCall,
+	Usage,
 } from "../types.js";
 
 export interface GoogleLLMOptions extends LLMOptions {
@@ -97,11 +98,12 @@ export class GoogleLLM implements LLM<GoogleLLMOptions> {
 			let thinking = "";
 			let thoughtSignature: string | undefined;
 			const toolCalls: ToolCall[] = [];
-			let usage: TokenUsage = {
+			let usage: Usage = {
 				input: 0,
 				output: 0,
 				cacheRead: 0,
 				cacheWrite: 0,
+				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			};
 			let stopReason: StopReason = "stop";
 			let inTextBlock = false;
@@ -179,6 +181,13 @@ export class GoogleLLM implements LLM<GoogleLLMOptions> {
 							(chunk.usageMetadata.candidatesTokenCount || 0) + (chunk.usageMetadata.thoughtsTokenCount || 0),
 						cacheRead: chunk.usageMetadata.cachedContentTokenCount || 0,
 						cacheWrite: 0,
+						cost: {
+							input: 0,
+							output: 0,
+							cacheRead: 0,
+							cacheWrite: 0,
+							total: 0,
+						},
 					};
 				}
 			}
@@ -203,6 +212,9 @@ export class GoogleLLM implements LLM<GoogleLLMOptions> {
 				thoughtSignature = Buffer.from(signature).toString("base64");
 			}
 
+			// Calculate cost
+			calculateCost(this.model, usage);
+
 			// Usage metadata is in the last chunk
 			// Already captured during streaming
 
@@ -227,6 +239,7 @@ export class GoogleLLM implements LLM<GoogleLLMOptions> {
 					output: 0,
 					cacheRead: 0,
 					cacheWrite: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 				},
 				stopReason: "error",
 				error: error instanceof Error ? error.message : String(error),

packages/ai/src/providers/openai-completions.ts

@@ -1,5 +1,6 @@
 import OpenAI from "openai";
 import type { ChatCompletionChunk, ChatCompletionMessageParam } from "openai/resources/chat/completions.js";
+import { calculateCost } from "../models.js";
 import type {
 	AssistantMessage,
 	Context,
@@ -8,9 +9,9 @@ import type {
 	Message,
 	Model,
 	StopReason,
-	TokenUsage,
 	Tool,
 	ToolCall,
+	Usage,
 } from "../types.js";
 
 export interface OpenAICompletionsLLMOptions extends LLMOptions {
@@ -87,11 +88,12 @@ export class OpenAICompletionsLLM implements LLM<OpenAICompletionsLLMOptions> {
 			let reasoningContent = "";
 			let reasoningField: "reasoning" | "reasoning_content" | null = null;
 			const parsedToolCalls: { id: string; name: string; arguments: string }[] = [];
-			let usage: TokenUsage = {
+			let usage: Usage = {
 				input: 0,
 				output: 0,
 				cacheRead: 0,
 				cacheWrite: 0,
+				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			};
 			let finishReason: ChatCompletionChunk.Choice["finish_reason"] | null = null;
 			let blockType: "text" | "thinking" | null = null;
@@ -104,6 +106,13 @@ export class OpenAICompletionsLLM implements LLM<OpenAICompletionsLLMOptions> {
 							(chunk.usage.completion_tokens_details?.reasoning_tokens || 0),
 						cacheRead: chunk.usage.prompt_tokens_details?.cached_tokens || 0,
 						cacheWrite: 0,
+						cost: {
+							input: 0,
+							output: 0,
+							cacheRead: 0,
+							cacheWrite: 0,
+							total: 0,
+						},
 					};
 				}
 
@@ -206,6 +215,9 @@ export class OpenAICompletionsLLM implements LLM<OpenAICompletionsLLMOptions> {
 				arguments: JSON.parse(tc.arguments),
 			}));
 
+			// Calculate cost
+			calculateCost(this.modelInfo, usage);
+
 			return {
 				role: "assistant",
 				content: content || undefined,
@@ -227,6 +239,7 @@ export class OpenAICompletionsLLM implements LLM<OpenAICompletionsLLMOptions> {
 					output: 0,
 					cacheRead: 0,
 					cacheWrite: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 				},
 				stopReason: "error",
 				error: error instanceof Error ? error.message : String(error),

packages/ai/src/providers/openai-responses.ts

@@ -13,9 +13,9 @@ import type {
 	Message,
 	Model,
 	StopReason,
-	TokenUsage,
 	Tool,
 	ToolCall,
+	Usage,
 } from "../types.js";
 
 export interface OpenAIResponsesLLMOptions extends LLMOptions {
@@ -83,11 +83,12 @@ export class OpenAIResponsesLLM implements LLM<OpenAIResponsesLLMOptions> {
 			let thinking = "";
 			const toolCalls: ToolCall[] = [];
 			const reasoningItems: ResponseReasoningItem[] = [];
-			let usage: TokenUsage = {
+			let usage: Usage = {
 				input: 0,
 				output: 0,
 				cacheRead: 0,
 				cacheWrite: 0,
+				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 			};
 			let stopReason: StopReason = "stop";
 
@@ -137,6 +138,7 @@ export class OpenAIResponsesLLM implements LLM<OpenAIResponsesLLMOptions> {
 							output: response.usage.output_tokens || 0,
 							cacheRead: response.usage.input_tokens_details?.cached_tokens || 0,
 							cacheWrite: 0,
+							cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 						};
 					}
 
@@ -180,6 +182,7 @@ export class OpenAIResponsesLLM implements LLM<OpenAIResponsesLLMOptions> {
 					output: 0,
 					cacheRead: 0,
 					cacheWrite: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
 				},
 				stopReason: "error",
 				error: error instanceof Error ? error.message : String(error),

packages/ai/src/types.ts

@@ -28,7 +28,7 @@ export interface AssistantMessage {
 	}[];
 	provider: string;
 	model: string;
-	usage: TokenUsage;
+	usage: Usage;
 
 	stopReason: StopReason;
 	error?: string | Error;
@@ -60,7 +60,7 @@ export type Event =
 	| { type: "text"; content: string; delta: string }
 	| { type: "thinking"; content: string; delta: string }
 	| { type: "toolCall"; toolCall: ToolCall }
-	| { type: "usage"; usage: TokenUsage }
+	| { type: "usage"; usage: Usage }
 	| { type: "done"; reason: StopReason; message: AssistantMessage }
 	| { type: "error"; error: Error };
 
@@ -70,12 +70,12 @@ export interface ToolCall {
 	arguments: Record<string, any>;
 }
 
-export interface TokenUsage {
+export interface Usage {
 	input: number;
 	output: number;
 	cacheRead: number;
 	cacheWrite: number;
-	cost?: {
+	cost: {
 		input: number;
 		output: number;
 		cacheRead: number;