diff --git a/src/__tests__/history-resume-delegation.spec.ts b/src/__tests__/history-resume-delegation.spec.ts
index a78c41b7c06..2436b6e9d24 100644
--- a/src/__tests__/history-resume-delegation.spec.ts
+++ b/src/__tests__/history-resume-delegation.spec.ts
@@ -241,7 +241,7 @@ describe("History resume delegation - parent metadata transitions", () => {
 						type: "tool_use",
 						name: "new_task",
 						id: "toolu_abc123",
-						input: { mode: "code", message: "Do something" },
+						input: { mode_slug: "code", message: "Do something" },
 					},
 				],
 				ts: 50,
diff --git a/src/core/assistant-message/NativeToolCallParser.ts b/src/core/assistant-message/NativeToolCallParser.ts
index bda7c71eb8d..35db134d669 100644
--- a/src/core/assistant-message/NativeToolCallParser.ts
+++ b/src/core/assistant-message/NativeToolCallParser.ts
@@ -628,9 +628,9 @@ export class NativeToolCallParser {
 				break
 
 			case "new_task":
-				if (partialArgs.mode !== undefined || partialArgs.message !== undefined) {
+				if (partialArgs.mode_slug !== undefined || partialArgs.message !== undefined) {
 					nativeArgs = {
-						mode: partialArgs.mode,
+						mode_slug: partialArgs.mode_slug,
 						message: partialArgs.message,
 						todos: partialArgs.todos,
 					}
@@ -977,9 +977,9 @@ export class NativeToolCallParser {
 					break
 
 				case "new_task":
-					if (args.mode !== undefined && args.message !== undefined) {
+					if (args.mode_slug !== undefined && args.message !== undefined) {
 						nativeArgs = {
-							mode: args.mode,
+							mode_slug: args.mode_slug,
 							message: args.message,
 							todos: args.todos,
 						} as NativeArgsFor<TName>
diff --git a/src/core/assistant-message/presentAssistantMessage.ts b/src/core/assistant-message/presentAssistantMessage.ts
index 7f5862be154..b060d0e3b05 100644
--- a/src/core/assistant-message/presentAssistantMessage.ts
+++ b/src/core/assistant-message/presentAssistantMessage.ts
@@ -372,7 +372,7 @@ export async function presentAssistantMessage(cline: Task) {
 					case "update_todo_list":
 						return `[${block.name}]`
 					case "new_task": {
-						const mode = block.params.mode ?? defaultModeSlug
+						const mode = block.params.mode_slug ?? defaultModeSlug
 						const message = block.params.message ?? "(no message)"
 						const modeName = getModeBySlug(mode, customModes)?.name ?? mode
 						return `[${block.name} in ${modeName} mode: '${message}']`
diff --git a/src/core/prompts/tools/native-tools/new_task.ts b/src/core/prompts/tools/native-tools/new_task.ts
index f8e29e549d9..e75c416cf70 100644
--- a/src/core/prompts/tools/native-tools/new_task.ts
+++ b/src/core/prompts/tools/native-tools/new_task.ts
@@ -19,7 +19,7 @@ export default {
 		parameters: {
 			type: "object",
 			properties: {
-				mode: {
+				mode_slug: {
 					type: "string",
 					description: MODE_PARAMETER_DESCRIPTION,
 				},
@@ -32,7 +32,7 @@ export default {
 					description: TODOS_PARAMETER_DESCRIPTION,
 				},
 			},
-			required: ["mode", "message", "todos"],
+			required: ["mode_slug", "message", "todos"],
 			additionalProperties: false,
 		},
 	},
diff --git a/src/core/task/__tests__/new-task-isolation.spec.ts b/src/core/task/__tests__/new-task-isolation.spec.ts
index 9100fb33993..0c3db509020 100644
--- a/src/core/task/__tests__/new-task-isolation.spec.ts
+++ b/src/core/task/__tests__/new-task-isolation.spec.ts
@@ -61,7 +61,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 			]
 
@@ -83,7 +83,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 			]
 
@@ -123,7 +123,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -146,7 +146,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -173,7 +173,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -219,7 +219,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -253,7 +253,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -284,7 +284,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "text",
@@ -316,7 +316,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				// Simulating a malformed tool without ID (shouldn't happen, but defensive)
 				{
@@ -345,13 +345,13 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "First task" },
+					input: { mode_slug: "code", message: "First task" },
 				},
 				{
 					type: "tool_use",
 					id: "toolu_new_task_2",
 					name: "new_task",
-					input: { mode: "debug", message: "Second task" },
+					input: { mode_slug: "debug", message: "Second task" },
 				},
 			]
 
@@ -375,7 +375,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
@@ -397,7 +397,7 @@ describe("new_task Tool Isolation Enforcement", () => {
 					type: "tool_use",
 					id: "toolu_new_task_1",
 					name: "new_task",
-					input: { mode: "code", message: "Do something" },
+					input: { mode_slug: "code", message: "Do something" },
 				},
 				{
 					type: "tool_use",
diff --git a/src/core/tools/NewTaskTool.ts b/src/core/tools/NewTaskTool.ts
index f36d8e1e379..acc80ab082c 100644
--- a/src/core/tools/NewTaskTool.ts
+++ b/src/core/tools/NewTaskTool.ts
@@ -12,7 +12,7 @@ import { BaseTool, ToolCallbacks } from "./BaseTool"
 import type { ToolUse } from "../../shared/tools"
 
 interface NewTaskParams {
-	mode: string
+	mode_slug: string
 	message: string
 	todos?: string
 }
@@ -21,16 +21,16 @@ export class NewTaskTool extends BaseTool<"new_task"> {
 	readonly name = "new_task" as const
 
 	async execute(params: NewTaskParams, task: Task, callbacks: ToolCallbacks): Promise<void> {
-		const { mode, message, todos } = params
+		const { mode_slug, message, todos } = params
 		const { askApproval, handleError, pushToolResult } = callbacks
 
 		try {
 			// Validate required parameters.
-			if (!mode) {
+			if (!mode_slug) {
 				task.consecutiveMistakeCount++
 				task.recordToolError("new_task")
 				task.didToolFailInCurrentTurn = true
-				pushToolResult(await task.sayAndCreateMissingParamError("new_task", "mode"))
+				pushToolResult(await task.sayAndCreateMissingParamError("new_task", "mode_slug"))
 				return
 			}
 
@@ -89,10 +89,10 @@ export class NewTaskTool extends BaseTool<"new_task"> {
 			const unescapedMessage = message.replace(/\\\\@/g, "\\@")
 
 			// Verify the mode exists
-			const targetMode = getModeBySlug(mode, state?.customModes)
+			const targetMode = getModeBySlug(mode_slug, state?.customModes)
 
 			if (!targetMode) {
-				pushToolResult(formatResponse.toolError(`Invalid mode: ${mode}`))
+				pushToolResult(formatResponse.toolError(`Invalid mode: ${mode_slug}`))
 				return
 			}
 
@@ -114,7 +114,7 @@ export class NewTaskTool extends BaseTool<"new_task"> {
 				parentTaskId: task.taskId,
 				message: unescapedMessage,
 				initialTodos: todoItems,
-				mode,
+				mode: mode_slug,
 			})
 
 			// Reflect delegation in tool result (no pause/unpause, no wait)
@@ -127,7 +127,7 @@ export class NewTaskTool extends BaseTool<"new_task"> {
 	}
 
 	override async handlePartial(task: Task, block: ToolUse<"new_task">): Promise<void> {
-		const mode: string | undefined = block.params.mode
+		const mode: string | undefined = block.params.mode_slug
 		const message: string | undefined = block.params.message
 		const todos: string | undefined = block.params.todos
 
diff --git a/src/core/tools/__tests__/newTaskTool.spec.ts b/src/core/tools/__tests__/newTaskTool.spec.ts
index fc383c13eef..6396def511f 100644
--- a/src/core/tools/__tests__/newTaskTool.spec.ts
+++ b/src/core/tools/__tests__/newTaskTool.spec.ts
@@ -117,7 +117,7 @@ const withNativeArgs = (block: ToolUse<"new_task">): ToolUse<"new_task"> => ({
 	// These tests intentionally exercise missing-param behavior, so we allow undefined
 	// values and let the tool's runtime validation handle it.
 	nativeArgs: {
-		mode: block.params.mode,
+		mode_slug: block.params.mode_slug,
 		message: block.params.message,
 		todos: block.params.todos,
 	} as unknown as NativeToolArgs["new_task"],
@@ -148,7 +148,7 @@ describe("newTaskTool", () => {
 			type: "tool_use", // Add required 'type' property
 			name: "new_task", // Correct property name
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Review this: \\\\@file1.txt and also \\\\\\\\@file2.txt", // Input with \\@ and \\\\@
 				todos: "[ ] First task\n[ ] Second task",
 			},
@@ -183,7 +183,7 @@ describe("newTaskTool", () => {
 			type: "tool_use", // Add required 'type' property
 			name: "new_task", // Correct property name
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "This is already unescaped: \\@file1.txt",
 				todos: "[ ] Test todo",
 			},
@@ -208,7 +208,7 @@ describe("newTaskTool", () => {
 			type: "tool_use", // Add required 'type' property
 			name: "new_task", // Correct property name
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "A normal mention @file1.txt",
 				todos: "[ ] Test todo",
 			},
@@ -233,7 +233,7 @@ describe("newTaskTool", () => {
 			type: "tool_use", // Add required 'type' property
 			name: "new_task", // Correct property name
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Mix: @file0.txt, \\@file1.txt, \\\\@file2.txt, \\\\\\\\@file3.txt",
 				todos: "[ ] Test todo",
 			},
@@ -258,7 +258,7 @@ describe("newTaskTool", () => {
 			type: "tool_use",
 			name: "new_task",
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Test message",
 				// todos missing - should work for backward compatibility
 			},
@@ -288,7 +288,7 @@ describe("newTaskTool", () => {
 			type: "tool_use",
 			name: "new_task",
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Test message with todos",
 				todos: "[ ] First task\n[ ] Second task",
 			},
@@ -332,7 +332,7 @@ describe("newTaskTool", () => {
 			pushToolResult: mockPushToolResult,
 		})
 
-		expect(mockSayAndCreateMissingParamError).toHaveBeenCalledWith("new_task", "mode")
+		expect(mockSayAndCreateMissingParamError).toHaveBeenCalledWith("new_task", "mode_slug")
 		expect(mockCline.consecutiveMistakeCount).toBe(1)
 		expect(mockCline.recordToolError).toHaveBeenCalledWith("new_task")
 	})
@@ -342,7 +342,7 @@ describe("newTaskTool", () => {
 			type: "tool_use",
 			name: "new_task",
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				// message missing
 				todos: "[ ] Test todo",
 			},
@@ -365,7 +365,7 @@ describe("newTaskTool", () => {
 			type: "tool_use",
 			name: "new_task",
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Test message",
 				todos: "[ ] Pending task\n[x] Completed task\n[-] In progress task",
 			},
@@ -401,7 +401,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 					// todos missing - should work when setting is disabled
 				},
@@ -437,7 +437,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 					// todos missing - should error when setting is enabled
 				},
@@ -473,7 +473,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 					todos: "[ ] First task\n[ ] Second task",
 				},
@@ -515,7 +515,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 					todos: "", // Empty string should be accepted
 				},
@@ -550,7 +550,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 				},
 				partial: false,
@@ -583,7 +583,7 @@ describe("newTaskTool", () => {
 				type: "tool_use",
 				name: "new_task",
 				params: {
-					mode: "code",
+					mode_slug: "code",
 					message: "Test message",
 				},
 				partial: false,
@@ -640,7 +640,7 @@ describe("newTaskTool delegation flow", () => {
 			type: "tool_use",
 			name: "new_task",
 			params: {
-				mode: "code",
+				mode_slug: "code",
 				message: "Do something",
 				// no todos -> should default to []
 			},
diff --git a/src/shared/tools.ts b/src/shared/tools.ts
index d2dd9907b17..52980e681fe 100644
--- a/src/shared/tools.ts
+++ b/src/shared/tools.ts
@@ -102,7 +102,7 @@ export type NativeToolArgs = {
 	edit_file: { file_path: string; old_string: string; new_string: string; expected_replacements?: number }
 	apply_patch: { patch: string }
 	list_files: { path: string; recursive?: boolean }
-	new_task: { mode: string; message: string; todos?: string }
+	new_task: { mode_slug: string; message: string; todos?: string }
 	ask_followup_question: {
 		question: string
 		follow_up: Array<{ text: string; mode?: string }>
@@ -240,7 +240,7 @@ export interface SwitchModeToolUse extends ToolUse<"switch_mode"> {
 
 export interface NewTaskToolUse extends ToolUse<"new_task"> {
 	name: "new_task"
-	params: Partial<Pick<Record<ToolParamName, string>, "mode" | "message" | "todos">>
+	params: Partial<Pick<Record<ToolParamName, string>, "mode_slug" | "message" | "todos">>
 }
 
 export interface RunSlashCommandToolUse extends ToolUse<"run_slash_command"> {