diff --git a/apps/cli/src/agent/__tests__/json-event-emitter-result.test.ts b/apps/cli/src/agent/__tests__/json-event-emitter-result.test.ts
index 2be7adcbb53..ffec8b64763 100644
--- a/apps/cli/src/agent/__tests__/json-event-emitter-result.test.ts
+++ b/apps/cli/src/agent/__tests__/json-event-emitter-result.test.ts
@@ -32,6 +32,13 @@ function emitMessage(emitter: JsonEventEmitter, message: ClineMessage): void {
 	)
 }
 
+function emitMessageUpdate(emitter: JsonEventEmitter, message: ClineMessage): void {
+	;(emitter as unknown as { handleMessage: (msg: ClineMessage, isUpdate: boolean) => void }).handleMessage(
+		message,
+		true,
+	)
+}
+
 function emitTaskCompleted(emitter: JsonEventEmitter, event: TaskCompletedEvent): void {
 	;(emitter as unknown as { handleTaskCompleted: (taskCompleted: TaskCompletedEvent) => void }).handleTaskCompleted(
 		event,
@@ -63,6 +70,178 @@ function createCompletedStateInfo(message: ClineMessage): AgentStateInfo {
 }
 
 describe("JsonEventEmitter result emission", () => {
+	it("reports context usage when context window is configured", () => {
+		const { stdout, lines } = createMockStdout()
+		const emitter = new JsonEventEmitter({ mode: "stream-json", stdout, contextWindow: 200 })
+
+		emitMessage(emitter, {
+			ts: 5,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				cost: 0.001,
+				tokensIn: 40,
+				tokensOut: 20,
+			}),
+		} as ClineMessage)
+
+		emitMessage(emitter, {
+			ts: 6,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				cost: 0.002,
+				tokensIn: 30,
+				tokensOut: 10,
+			}),
+		} as ClineMessage)
+
+		const completionMessage = createAskCompletionMessage(7, "done")
+		emitTaskCompleted(emitter, {
+			success: true,
+			stateInfo: createCompletedStateInfo(completionMessage),
+			message: completionMessage,
+		})
+
+		const result = lines().find((line) => line.type === "result")
+		const cost = result?.cost as Record<string, unknown>
+
+		expect(cost?.contextWindow).toBe(200)
+		expect(cost?.contextTokens).toBe(40)
+		expect(cost?.contextUsagePercent).toBe(20)
+	})
+
+	it("reports token usage and context usage when api_req_started has no cost field", () => {
+		const { stdout, lines } = createMockStdout()
+		const emitter = new JsonEventEmitter({ mode: "stream-json", stdout, contextWindow: 1000 })
+
+		emitMessage(emitter, {
+			ts: 8,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				tokensIn: 120,
+				tokensOut: 30,
+				cacheWrites: 10,
+				cacheReads: 5,
+			}),
+		} as ClineMessage)
+
+		const completionMessage = createAskCompletionMessage(9, "done")
+		emitTaskCompleted(emitter, {
+			success: true,
+			stateInfo: createCompletedStateInfo(completionMessage),
+			message: completionMessage,
+		})
+
+		const result = lines().find((line) => line.type === "result")
+		const cost = result?.cost as Record<string, unknown>
+
+		expect(cost?.inputTokens).toBe(120)
+		expect(cost?.outputTokens).toBe(30)
+		expect(cost?.cacheWrites).toBe(10)
+		expect(cost?.cacheReads).toBe(5)
+		expect(cost).not.toHaveProperty("totalCost")
+		expect(cost?.contextTokens).toBe(150)
+		expect(cost?.contextWindow).toBe(1000)
+		expect(cost?.contextUsagePercent).toBe(15)
+	})
+
+	it("aggregates token usage and cost across api requests in a completion turn", () => {
+		const { stdout, lines } = createMockStdout()
+		const emitter = new JsonEventEmitter({ mode: "stream-json", stdout })
+
+		emitMessage(emitter, {
+			ts: 10,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				cost: 0.01,
+				tokensIn: 100,
+				tokensOut: 50,
+				cacheWrites: 20,
+				cacheReads: 10,
+			}),
+		} as ClineMessage)
+
+		emitMessage(emitter, {
+			ts: 11,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				cost: 0.02,
+				tokensIn: 25,
+				tokensOut: 10,
+				cacheWrites: 5,
+				cacheReads: 2,
+			}),
+		} as ClineMessage)
+
+		const completionMessage = createAskCompletionMessage(12, "done")
+		emitTaskCompleted(emitter, {
+			success: true,
+			stateInfo: createCompletedStateInfo(completionMessage),
+			message: completionMessage,
+		})
+
+		const result = lines().find((line) => line.type === "result")
+		expect(result).toBeDefined()
+		expect(result?.cost).toMatchObject({
+			totalCost: 0.03,
+			inputTokens: 125,
+			outputTokens: 60,
+			cacheWrites: 25,
+			cacheReads: 12,
+		})
+	})
+
+	it("captures cost from updated api_req_started messages with the same message id", () => {
+		const { stdout, lines } = createMockStdout()
+		const emitter = new JsonEventEmitter({ mode: "stream-json", stdout })
+
+		// Placeholder message without final usage.
+		emitMessage(emitter, {
+			ts: 20,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({ apiProtocol: "openai" }),
+		} as ClineMessage)
+
+		// Later update of the same message with finalized usage/cost.
+		emitMessageUpdate(emitter, {
+			ts: 20,
+			type: "say",
+			say: "api_req_started",
+			partial: false,
+			text: JSON.stringify({
+				apiProtocol: "openai",
+				cost: 0.004,
+				tokensIn: 40,
+				tokensOut: 10,
+			}),
+		} as ClineMessage)
+
+		const completionMessage = createAskCompletionMessage(21, "done")
+		emitTaskCompleted(emitter, {
+			success: true,
+			stateInfo: createCompletedStateInfo(completionMessage),
+			message: completionMessage,
+		})
+
+		const result = lines().find((line) => line.type === "result")
+		expect(result?.cost).toMatchObject({
+			totalCost: 0.004,
+			inputTokens: 40,
+			outputTokens: 10,
+		})
+	})
+
 	it("prefers current completion message content over stale cached completion text", () => {
 		const { stdout, lines } = createMockStdout()
 		const emitter = new JsonEventEmitter({ mode: "stream-json", stdout })
@@ -125,5 +304,6 @@ describe("JsonEventEmitter result emission", () => {
 		expect(output).toHaveLength(2)
 		expect(output[0]?.content).toBe("FIRST")
 		expect(output[1]).not.toHaveProperty("content")
+		expect(output[1]).not.toHaveProperty("cost")
 	})
 })
diff --git a/apps/cli/src/agent/json-event-emitter.ts b/apps/cli/src/agent/json-event-emitter.ts
index f46c39be506..abc030e7040 100644
--- a/apps/cli/src/agent/json-event-emitter.ts
+++ b/apps/cli/src/agent/json-event-emitter.ts
@@ -38,6 +38,8 @@ export interface JsonEventEmitterOptions {
 	protocol?: string
 	/** Supported stdin protocol capabilities emitted in system:init */
 	capabilities?: string[]
+	/** Optional context window for reporting context usage in result.cost */
+	contextWindow?: number
 }
 
 /**
@@ -55,21 +57,31 @@ function parseToolInfo(text: string | undefined): { name: string; input: Record<
 }
 
 /**
- * Parse API request cost information from api_req_started message text.
+ * Parse API request usage information from api_req_started message text.
  */
 function parseApiReqCost(text: string | undefined): JsonEventCost | undefined {
 	if (!text) return undefined
 	try {
 		const parsed = JSON.parse(text)
-		return parsed.cost !== undefined
-			? {
-					totalCost: parsed.cost,
-					inputTokens: parsed.tokensIn,
-					outputTokens: parsed.tokensOut,
-					cacheWrites: parsed.cacheWrites,
-					cacheReads: parsed.cacheReads,
-				}
-			: undefined
+		const usage: JsonEventCost = {}
+
+		if (typeof parsed.cost === "number") {
+			usage.totalCost = parsed.cost
+		}
+		if (typeof parsed.tokensIn === "number") {
+			usage.inputTokens = parsed.tokensIn
+		}
+		if (typeof parsed.tokensOut === "number") {
+			usage.outputTokens = parsed.tokensOut
+		}
+		if (typeof parsed.cacheWrites === "number") {
+			usage.cacheWrites = parsed.cacheWrites
+		}
+		if (typeof parsed.cacheReads === "number") {
+			usage.cacheReads = parsed.cacheReads
+		}
+
+		return Object.keys(usage).length > 0 ? usage : undefined
 	} catch {
 		return undefined
 	}
@@ -97,12 +109,14 @@ export class JsonEventEmitter {
 	private events: JsonEvent[] = []
 	private unsubscribers: (() => void)[] = []
 	private pendingWrites = new Set<Promise<void>>()
-	private lastCost: JsonEventCost | undefined
 	private requestIdProvider: () => string | undefined
 	private schemaVersion: number
 	private protocol: string
 	private capabilities: string[]
+	private contextWindow: number | undefined
 	private seenMessageIds = new Set<number>()
+	// Track finalized api_req_started usage for the current completion turn.
+	private currentTurnApiReqCosts = new Map<number, JsonEventCost>()
 	// Track previous content for delta computation
 	private previousContent = new Map<number, string>()
 	// Track previous tool-use content for structured (non-append-only) delta computation.
@@ -127,6 +141,19 @@ export class JsonEventEmitter {
 			"stdin:ping",
 			"stdin:shutdown",
 		]
+		this.contextWindow =
+			typeof options.contextWindow === "number" &&
+			Number.isFinite(options.contextWindow) &&
+			options.contextWindow > 0
+				? options.contextWindow
+				: undefined
+	}
+
+	setContextWindow(contextWindow: number | undefined): void {
+		this.contextWindow =
+			typeof contextWindow === "number" && Number.isFinite(contextWindow) && contextWindow > 0
+				? contextWindow
+				: undefined
 	}
 
 	/**
@@ -326,6 +353,84 @@ export class JsonEventEmitter {
 		return event
 	}
 
+	private updateCurrentTurnApiCost(msgId: number, cost: JsonEventCost): void {
+		this.currentTurnApiReqCosts.set(msgId, cost)
+	}
+
+	private getCurrentTurnCost(): JsonEventCost | undefined {
+		if (this.currentTurnApiReqCosts.size === 0) {
+			return undefined
+		}
+
+		let totalCost = 0
+		let inputTokens = 0
+		let outputTokens = 0
+		let cacheWrites = 0
+		let cacheReads = 0
+
+		let hasTotalCost = false
+		let hasInputTokens = false
+		let hasOutputTokens = false
+		let hasCacheWrites = false
+		let hasCacheReads = false
+
+		for (const value of this.currentTurnApiReqCosts.values()) {
+			if (typeof value.totalCost === "number") {
+				totalCost += value.totalCost
+				hasTotalCost = true
+			}
+			if (typeof value.inputTokens === "number") {
+				inputTokens += value.inputTokens
+				hasInputTokens = true
+			}
+			if (typeof value.outputTokens === "number") {
+				outputTokens += value.outputTokens
+				hasOutputTokens = true
+			}
+			if (typeof value.cacheWrites === "number") {
+				cacheWrites += value.cacheWrites
+				hasCacheWrites = true
+			}
+			if (typeof value.cacheReads === "number") {
+				cacheReads += value.cacheReads
+				hasCacheReads = true
+			}
+		}
+
+		const aggregated: JsonEventCost = {}
+		if (hasTotalCost) aggregated.totalCost = totalCost
+		if (hasInputTokens) aggregated.inputTokens = inputTokens
+		if (hasOutputTokens) aggregated.outputTokens = outputTokens
+		if (hasCacheWrites) aggregated.cacheWrites = cacheWrites
+		if (hasCacheReads) aggregated.cacheReads = cacheReads
+
+		if (this.contextWindow !== undefined) {
+			let latestMessageId = Number.NEGATIVE_INFINITY
+			let latestRequestCost: JsonEventCost | undefined
+
+			for (const [messageId, usage] of this.currentTurnApiReqCosts.entries()) {
+				if (messageId > latestMessageId) {
+					latestMessageId = messageId
+					latestRequestCost = usage
+				}
+			}
+
+			if (latestRequestCost) {
+				const contextTokensIn =
+					typeof latestRequestCost.inputTokens === "number" ? latestRequestCost.inputTokens : 0
+				const contextTokensOut =
+					typeof latestRequestCost.outputTokens === "number" ? latestRequestCost.outputTokens : 0
+				const contextTokens = contextTokensIn + contextTokensOut
+
+				aggregated.contextTokens = contextTokens
+				aggregated.contextWindow = this.contextWindow
+				aggregated.contextUsagePercent = (contextTokens / this.contextWindow) * 100
+			}
+		}
+
+		return Object.keys(aggregated).length > 0 ? aggregated : undefined
+	}
+
 	/**
 	 * Handle a ClineMessage and emit the appropriate JSON event.
 	 */
@@ -339,6 +444,14 @@ export class JsonEventEmitter {
 
 		// Skip duplicate complete messages
 		if (isDone && this.seenMessageIds.has(msg.ts)) {
+			// api_req_started messages are updated in-place (same ts) with final usage/cost.
+			// We still need to process those updates for result metrics, even if we skip re-emitting.
+			if (msg.type === "say" && msg.say === "api_req_started") {
+				const cost = parseApiReqCost(msg.text)
+				if (cost) {
+					this.updateCurrentTurnApiCost(msg.ts, cost)
+				}
+			}
 			return
 		}
 
@@ -409,7 +522,7 @@ export class JsonEventEmitter {
 			case "api_req_started": {
 				const cost = parseApiReqCost(msg.text)
 				if (cost) {
-					this.lastCost = cost
+					this.updateCurrentTurnApiCost(msg.ts, cost)
 				}
 				break
 			}
@@ -602,6 +715,7 @@ export class JsonEventEmitter {
 		// Prefer the completion payload from the current event. If it is empty,
 		// fall back to the most recent tracked completion text, then assistant text.
 		const resultContent = event.message?.text || this.completionResultContent || this.lastAssistantText
+		const resultCost = this.getCurrentTurnCost()
 
 		this.emitEvent({
 			type: "result",
@@ -609,16 +723,17 @@ export class JsonEventEmitter {
 			content: resultContent,
 			done: true,
 			success: event.success,
-			cost: this.lastCost,
+			cost: resultCost,
 		})
 
 		// Prevent stale completion content from leaking into later turns.
 		this.completionResultContent = undefined
 		this.lastAssistantText = undefined
+		this.currentTurnApiReqCosts.clear()
 
 		// For "json" mode, output the final accumulated result
 		if (this.mode === "json") {
-			this.outputFinalResult(event.success, resultContent)
+			this.outputFinalResult(event.success, resultContent, resultCost)
 		}
 	}
 
@@ -659,12 +774,12 @@ export class JsonEventEmitter {
 	/**
 	 * Output the final accumulated result (for "json" mode).
 	 */
-	private outputFinalResult(success: boolean, content?: string): void {
+	private outputFinalResult(success: boolean, content?: string, cost?: JsonEventCost): void {
 		const output: JsonFinalOutput = {
 			type: "result",
 			success,
 			content,
-			cost: this.lastCost,
+			cost,
 			events: this.events.filter((e) => e.type !== "result"), // Exclude the result event itself
 		}
 
@@ -707,10 +822,10 @@ export class JsonEventEmitter {
 	 */
 	clear(): void {
 		this.events = []
-		this.lastCost = undefined
 		this.seenMessageIds.clear()
 		this.previousContent.clear()
 		this.previousToolUseContent.clear()
+		this.currentTurnApiReqCosts.clear()
 		this.completionResultContent = undefined
 		this.lastAssistantText = undefined
 		this.expectPromptEchoAsUser = true
diff --git a/apps/cli/src/commands/cli/run.ts b/apps/cli/src/commands/cli/run.ts
index f2c0e039129..af97ffbf69d 100644
--- a/apps/cli/src/commands/cli/run.ts
+++ b/apps/cli/src/commands/cli/run.ts
@@ -6,6 +6,7 @@ import { createElement } from "react"
 import pWaitFor from "p-wait-for"
 
 import { setLogger } from "@roo-code/vscode-shim"
+import type { ModelRecord } from "@roo-code/types"
 
 import {
 	FlagOptions,
@@ -51,8 +52,8 @@ function normalizeError(error: unknown): Error {
 	return error instanceof Error ? error : new Error(String(error))
 }
 
-async function warmRooModels(host: ExtensionHost): Promise<void> {
-	await new Promise<void>((resolve, reject) => {
+async function fetchRooModels(host: ExtensionHost): Promise<ModelRecord> {
+	return new Promise<ModelRecord>((resolve, reject) => {
 		let settled = false
 
 		const cleanup = () => {
@@ -92,7 +93,7 @@ async function warmRooModels(host: ExtensionHost): Promise<void> {
 				return
 			}
 
-			finish(() => resolve())
+			finish(() => resolve(isRecord(values?.models) ? (values.models as ModelRecord) : {}))
 		}
 
 		const timeoutId = setTimeout(() => {
@@ -104,6 +105,14 @@ async function warmRooModels(host: ExtensionHost): Promise<void> {
 	})
 }
 
+function resolveRooModelContextWindow(models: ModelRecord, modelId: string): number | undefined {
+	const contextWindow = models[modelId]?.contextWindow
+	if (typeof contextWindow !== "number" || !Number.isFinite(contextWindow) || contextWindow <= 0) {
+		return undefined
+	}
+	return contextWindow
+}
+
 export async function run(promptArg: string | undefined, flagOptions: FlagOptions) {
 	setLogger({
 		info: () => {},
@@ -541,9 +550,18 @@ export async function run(promptArg: string | undefined, flagOptions: FlagOption
 
 		try {
 			await host.activate()
+			let rooContextWindow: number | undefined
+
 			if (extensionHostOptions.provider === "roo") {
 				try {
-					await warmRooModels(host)
+					const rooModels = await fetchRooModels(host)
+					rooContextWindow = resolveRooModelContextWindow(rooModels, extensionHostOptions.model)
+
+					if (flagOptions.debug && rooContextWindow === undefined) {
+						console.error(
+							`[CLI] Warning: Roo model context window unavailable for model: ${extensionHostOptions.model}`,
+						)
+					}
 				} catch (warmupError) {
 					if (flagOptions.debug) {
 						const message = warmupError instanceof Error ? warmupError.message : String(warmupError)
@@ -552,6 +570,10 @@ export async function run(promptArg: string | undefined, flagOptions: FlagOption
 				}
 			}
 
+			if (rooContextWindow !== undefined) {
+				jsonEmitter?.setContextWindow(rooContextWindow)
+			}
+
 			if (jsonEmitter) {
 				jsonEmitter.attachToClient(host.client)
 			}
diff --git a/packages/types/src/__tests__/cli.test.ts b/packages/types/src/__tests__/cli.test.ts
index 483e633b4c9..11300e93643 100644
--- a/packages/types/src/__tests__/cli.test.ts
+++ b/packages/types/src/__tests__/cli.test.ts
@@ -76,5 +76,28 @@ describe("CLI types", () => {
 
 			expect(result.success).toBe(true)
 		})
+
+		it("preserves context usage fields in result cost", () => {
+			const result = rooCliFinalOutputSchema.safeParse({
+				type: "result",
+				success: true,
+				cost: {
+					totalCost: 0.01,
+					inputTokens: 100,
+					outputTokens: 50,
+					contextTokens: 150,
+					contextWindow: 200_000,
+					contextUsagePercent: 0.075,
+				},
+				events: [],
+			})
+
+			expect(result.success).toBe(true)
+			if (result.success) {
+				expect(result.data.cost?.contextTokens).toBe(150)
+				expect(result.data.cost?.contextWindow).toBe(200_000)
+				expect(result.data.cost?.contextUsagePercent).toBe(0.075)
+			}
+		})
 	})
 })
diff --git a/packages/types/src/cli.ts b/packages/types/src/cli.ts
index 738db4a103e..042c3e7739f 100644
--- a/packages/types/src/cli.ts
+++ b/packages/types/src/cli.ts
@@ -125,6 +125,9 @@ export const rooCliCostSchema = z.object({
 	outputTokens: z.number().optional(),
 	cacheWrites: z.number().optional(),
 	cacheReads: z.number().optional(),
+	contextTokens: z.number().optional(),
+	contextWindow: z.number().optional(),
+	contextUsagePercent: z.number().optional(),
 })
 
 export type RooCliCost = z.infer<typeof rooCliCostSchema>