diff --git a/extensions/copilot/src/extension/intents/node/toolCallingLoop.ts b/extensions/copilot/src/extension/intents/node/toolCallingLoop.ts
index 704a19c3f1c..95fe25d8896 100644
--- a/extensions/copilot/src/extension/intents/node/toolCallingLoop.ts
+++ b/extensions/copilot/src/extension/intents/node/toolCallingLoop.ts
@@ -558,18 +558,6 @@ export abstract class ToolCallingLoop<TOptions extends IToolCallingLoopOptions =
 		let stopHookActive = false;
 		const sessionId = this.options.conversation.sessionId;
 
-		// Execute SubagentStart hook for subagent requests to get additional context
-		if (this.options.request.subAgentInvocationId) {
-			const startHookResult = await this.executeSubagentStartHook({
-				agent_id: this.options.request.subAgentInvocationId,
-				agent_type: this.options.request.subAgentName ?? 'default',
-			}, sessionId, outputStream, token);
-			if (startHookResult.additionalContext) {
-				this.additionalHookContext = startHookResult.additionalContext;
-				this._logService.info(`[ToolCallingLoop] SubagentStart hook provided context for subagent ${this.options.request.subAgentInvocationId}`);
-			}
-		}
-
 		while (true) {
 			if (lastResult && i++ >= this.options.toolCallLimit) {
 				lastResult = this.hitToolCallLimit(outputStream, lastResult);
diff --git a/extensions/copilot/src/extension/intents/test/node/toolCallingLoopHooks.spec.ts b/extensions/copilot/src/extension/intents/test/node/toolCallingLoopHooks.spec.ts
index 30dae2b8a02..0b255b8d92f 100644
--- a/extensions/copilot/src/extension/intents/test/node/toolCallingLoopHooks.spec.ts
+++ b/extensions/copilot/src/extension/intents/test/node/toolCallingLoopHooks.spec.ts
@@ -614,6 +614,36 @@ describe('ToolCallingLoop SubagentStart hook', () => {
 			const input = subagentStartCalls[0].input as SubagentStartHookInput;
 			expect(input.agent_type).toBe('default');
 		});
+
+		it('should execute SubagentStart hook only once when runStartHooks and run are both called', async () => {
+			const conversation = createTestConversation(1);
+			const request = createMockChatRequest({
+				subAgentInvocationId: 'subagent-dedup',
+				subAgentName: 'DedupAgent',
+			} as Partial<ChatRequest>);
+
+			const loop = instantiationService.createInstance(
+				TestToolCallingLoop,
+				{
+					conversation,
+					toolCallLimit: 10,
+					request,
+				}
+			);
+			disposables.add(loop);
+
+			// First call: runStartHooks should execute SubagentStart once
+			await loop.testRunStartHooks(tokenSource.token);
+
+			// Second call: run() should NOT execute SubagentStart again
+			// run() will throw because fetch() is not implemented, but SubagentStart
+			// happens before fetch, so we need to verify it wasn't called again
+			await expect(loop.run(undefined, tokenSource.token)).rejects.toThrow();
+
+			// SubagentStart should have been called exactly once (from runStartHooks only)
+			const subagentStartCalls = mockChatHookService.getCallsForHook('SubagentStart');
+			expect(subagentStartCalls).toHaveLength(1);
+		});
 	});
 
 	describe('SubagentStart hook result collection', () => {