diff --git a/src/shared/protocol.ts b/src/shared/protocol.ts
index aa242a647..c0670c4e9 100644
--- a/src/shared/protocol.ts
+++ b/src/shared/protocol.ts
@@ -265,7 +265,7 @@ export type RequestHandlerExtra<SendRequestT extends Request, SendNotificationT
 
     taskStore?: RequestTaskStore;
 
-    taskRequestedTtl?: number | null;
+    taskRequestedTtl?: number;
 
     /**
      * The original HTTP request.
diff --git a/src/types.ts b/src/types.ts
index 6bec5190c..864e3f9b4 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -35,10 +35,9 @@ export const CursorSchema = z.string();
  */
 export const TaskCreationParamsSchema = z.looseObject({
     /**
-     * Time in milliseconds to keep task results available after completion.
-     * If null, the task has unlimited lifetime until manually cleaned up.
+     * Requested duration in milliseconds to retain task from creation.
      */
-    ttl: z.union([z.number(), z.null()]).optional(),
+    ttl: z.number().optional(),
 
     /**
      * Time in milliseconds to wait between task status requests.
diff --git a/test/experimental/tasks/stores/in-memory.test.ts b/test/experimental/tasks/stores/in-memory.test.ts
index ceef6c6d8..fd6bddc93 100644
--- a/test/experimental/tasks/stores/in-memory.test.ts
+++ b/test/experimental/tasks/stores/in-memory.test.ts
@@ -487,17 +487,16 @@ describe('InMemoryTaskStore', () => {
             expect(task).toBeNull();
         });
 
-        it('should support null TTL for unlimited lifetime', async () => {
-            // Test that null TTL means unlimited lifetime
-            const taskParams: TaskCreationParams = {
-                ttl: null
-            };
+        it('should support omitted TTL for unlimited lifetime', async () => {
+            // Test that omitting TTL means unlimited lifetime (server returns null)
+            // Per spec: clients omit ttl to let server decide, server returns null for unlimited
+            const taskParams: TaskCreationParams = {};
             const createdTask = await store.createTask(taskParams, 2222, {
                 method: 'tools/call',
                 params: {}
             });
 
-            // The returned task should have null TTL
+            // The returned task should have null TTL (unlimited)
             expect(createdTask.ttl).toBeNull();
 
             // Task should not be cleaned up even after a long time
diff --git a/test/experimental/tasks/task.test.ts b/test/experimental/tasks/task.test.ts
index 37e3938d2..de613a325 100644
--- a/test/experimental/tasks/task.test.ts
+++ b/test/experimental/tasks/task.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect } from 'vitest';
 import { isTerminal } from '../../../src/experimental/tasks/interfaces.js';
 import type { Task } from '../../../src/types.js';
+import { TaskCreationParamsSchema } from '../../../src/types.js';
 
 describe('Task utility functions', () => {
     describe('isTerminal', () => {
@@ -115,3 +116,30 @@ describe('Task Schema Validation', () => {
         });
     });
 });
+
+describe('TaskCreationParams Schema Validation', () => {
+    it('should accept ttl as a number', () => {
+        const result = TaskCreationParamsSchema.safeParse({ ttl: 60000 });
+        expect(result.success).toBe(true);
+    });
+
+    it('should accept missing ttl (optional)', () => {
+        const result = TaskCreationParamsSchema.safeParse({});
+        expect(result.success).toBe(true);
+    });
+
+    it('should reject null ttl (not allowed in request, only response)', () => {
+        const result = TaskCreationParamsSchema.safeParse({ ttl: null });
+        expect(result.success).toBe(false);
+    });
+
+    it('should accept pollInterval as a number', () => {
+        const result = TaskCreationParamsSchema.safeParse({ pollInterval: 1000 });
+        expect(result.success).toBe(true);
+    });
+
+    it('should accept both ttl and pollInterval', () => {
+        const result = TaskCreationParamsSchema.safeParse({ ttl: 60000, pollInterval: 1000 });
+        expect(result.success).toBe(true);
+    });
+});