diff --git a/src/ModelContextProtocol.Core/Protocol/CreateTaskResult.cs b/src/ModelContextProtocol.Core/Protocol/CreateTaskResult.cs
index 2e5bc0c41..6d9bac23c 100644
--- a/src/ModelContextProtocol.Core/Protocol/CreateTaskResult.cs
+++ b/src/ModelContextProtocol.Core/Protocol/CreateTaskResult.cs
@@ -55,10 +55,11 @@ public sealed class CreateTaskResult : Result
     public required DateTimeOffset LastUpdatedAt { get; set; }
 
     /// <summary>
-    /// Gets or sets the time-to-live duration from creation in milliseconds, or <see langword="null"/> for unlimited.
+    /// Gets or sets the time-to-live duration from creation, or <see langword="null"/> for unlimited.
     /// </summary>
     [JsonPropertyName("ttlMs")]
-    public long? TtlMs { get; set; }
+    [JsonConverter(typeof(TimeSpanMillisecondsConverter))]
+    public TimeSpan? TimeToLive { get; set; }
 
     /// <summary>
     /// Gets or sets the suggested polling interval in milliseconds.
diff --git a/src/ModelContextProtocol.Core/Protocol/GetTaskResult.cs b/src/ModelContextProtocol.Core/Protocol/GetTaskResult.cs
index 9366f2374..3fea8cc6b 100644
--- a/src/ModelContextProtocol.Core/Protocol/GetTaskResult.cs
+++ b/src/ModelContextProtocol.Core/Protocol/GetTaskResult.cs
@@ -64,10 +64,10 @@ private protected GetTaskResult()
     public required DateTimeOffset LastUpdatedAt { get; set; }
 
     /// <summary>
-    /// Gets or sets the time-to-live duration from creation in milliseconds, or <see langword="null"/> for unlimited.
+    /// Gets or sets the time-to-live duration from creation, or <see langword="null"/> for unlimited.
     /// </summary>
     [JsonPropertyName("ttlMs")]
-    public long? TtlMs { get; set; }
+    public TimeSpan? TimeToLive { get; set; }
 
     /// <summary>
     /// Gets or sets the suggested polling interval in milliseconds.
@@ -245,7 +245,7 @@ internal sealed class Converter : JsonConverter<GetTaskResult>
             };
 
             taskResult.StatusMessage = statusMessage;
-            taskResult.TtlMs = ttlMs;
+            taskResult.TimeToLive = ttlMs is null ? null : TimeSpan.FromMilliseconds(ttlMs.Value);
             taskResult.PollIntervalMs = pollIntervalMs;
             taskResult.ResultType = resultType;
             taskResult.Meta = meta;
@@ -287,9 +287,9 @@ public override void Write(Utf8JsonWriter writer, GetTaskResult value, JsonSeria
             writer.WriteString("createdAt", value.CreatedAt);
             writer.WriteString("lastUpdatedAt", value.LastUpdatedAt);
 
-            if (value.TtlMs is not null)
+            if (value.TimeToLive is not null)
             {
-                writer.WriteNumber("ttlMs", value.TtlMs.Value);
+                writer.WriteNumber("ttlMs", (long)value.TimeToLive.Value.TotalMilliseconds);
             }
 
             if (value.PollIntervalMs is not null)
diff --git a/src/ModelContextProtocol.Core/Protocol/TaskStatusNotificationParams.cs b/src/ModelContextProtocol.Core/Protocol/TaskStatusNotificationParams.cs
index e1bbb2f73..4e859a22c 100644
--- a/src/ModelContextProtocol.Core/Protocol/TaskStatusNotificationParams.cs
+++ b/src/ModelContextProtocol.Core/Protocol/TaskStatusNotificationParams.cs
@@ -70,10 +70,10 @@ private protected TaskStatusNotificationParams()
     public required DateTimeOffset LastUpdatedAt { get; set; }
 
     /// <summary>
-    /// Gets or sets the time-to-live duration from creation in milliseconds, or <see langword="null"/> for unlimited.
+    /// Gets or sets the time-to-live duration from creation, or <see langword="null"/> for unlimited.
     /// </summary>
     [JsonPropertyName("ttlMs")]
-    public long? TtlMs { get; set; }
+    public TimeSpan? TimeToLive { get; set; }
 
     /// <summary>
     /// Gets or sets the suggested polling interval in milliseconds.
@@ -247,7 +247,7 @@ internal sealed class Converter : JsonConverter<TaskStatusNotificationParams>
             };
 
             notification.StatusMessage = statusMessage;
-            notification.TtlMs = ttlMs;
+            notification.TimeToLive = ttlMs is null ? null : TimeSpan.FromMilliseconds(ttlMs.Value);
             notification.PollIntervalMs = pollIntervalMs;
             notification.Meta = meta;
 
@@ -283,9 +283,9 @@ public override void Write(Utf8JsonWriter writer, TaskStatusNotificationParams v
             writer.WriteString("createdAt", value.CreatedAt);
             writer.WriteString("lastUpdatedAt", value.LastUpdatedAt);
 
-            if (value.TtlMs is not null)
+            if (value.TimeToLive is not null)
             {
-                writer.WriteNumber("ttlMs", value.TtlMs.Value);
+                writer.WriteNumber("ttlMs", (long)value.TimeToLive.Value.TotalMilliseconds);
             }
 
             if (value.PollIntervalMs is not null)
diff --git a/src/ModelContextProtocol.Core/Protocol/TimeSpanMillisecondsConverter.cs b/src/ModelContextProtocol.Core/Protocol/TimeSpanMillisecondsConverter.cs
new file mode 100644
index 000000000..9ad646b48
--- /dev/null
+++ b/src/ModelContextProtocol.Core/Protocol/TimeSpanMillisecondsConverter.cs
@@ -0,0 +1,19 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Provides a JSON converter for <see cref="TimeSpan"/> values that serializes and deserializes
+/// them as a whole-millisecond integer.
+/// </summary>
+public sealed class TimeSpanMillisecondsConverter : JsonConverter<TimeSpan>
+{
+    /// <inheritdoc />
+    public override TimeSpan Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => TimeSpan.FromMilliseconds(reader.GetDouble());
+
+    /// <inheritdoc />
+    public override void Write(Utf8JsonWriter writer, TimeSpan value, JsonSerializerOptions options)
+        => writer.WriteNumberValue((long)value.TotalMilliseconds);
+}
diff --git a/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs b/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs
index a13af13e9..00c69844b 100644
--- a/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs
+++ b/src/ModelContextProtocol.Core/Server/InMemoryMcpTaskStore.cs
@@ -32,9 +32,9 @@ public class InMemoryMcpTaskStore : IMcpTaskStore
     public long DefaultPollIntervalMs { get; set; } = 1000;
 
     /// <summary>
-    /// Gets or sets the default time-to-live in milliseconds for new tasks, or <see langword="null"/> for unlimited.
+    /// Gets or sets the default time-to-live for new tasks, or <see langword="null"/> for unlimited.
     /// </summary>
-    public long? DefaultTtlMs { get; set; }
+    public TimeSpan? DefaultTimeToLive { get; set; }
 
     /// <inheritdoc/>
     public Task<McpTaskInfo> CreateTaskAsync(CancellationToken cancellationToken = default)
@@ -42,7 +42,7 @@ public Task<McpTaskInfo> CreateTaskAsync(CancellationToken cancellationToken = d
         var taskId = Guid.NewGuid().ToString("N");
         var now = DateTimeOffset.UtcNow;
 
-        var info = new McpTaskInfo(taskId, McpTaskStatus.Working, now, now, DefaultTtlMs, DefaultPollIntervalMs);
+        var info = new McpTaskInfo(taskId, McpTaskStatus.Working, now, now, DefaultTimeToLive, DefaultPollIntervalMs);
         _tasks[taskId] = info;
 
         return Task.FromResult(info);
diff --git a/src/ModelContextProtocol.Core/Server/McpServerImpl.cs b/src/ModelContextProtocol.Core/Server/McpServerImpl.cs
index 85b1cc26a..1cce71c70 100644
--- a/src/ModelContextProtocol.Core/Server/McpServerImpl.cs
+++ b/src/ModelContextProtocol.Core/Server/McpServerImpl.cs
@@ -1009,7 +1009,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
         Status = info.Status,
         CreatedAt = info.CreatedAt,
         LastUpdatedAt = info.LastUpdatedAt,
-        TtlMs = info.TtlMs,
+        TimeToLive = info.TimeToLive,
         PollIntervalMs = info.PollIntervalMs,
         StatusMessage = info.StatusMessage,
         ResultType = "task",
@@ -1022,7 +1022,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
             TaskId = info.TaskId,
             CreatedAt = info.CreatedAt,
             LastUpdatedAt = info.LastUpdatedAt,
-            TtlMs = info.TtlMs,
+            TimeToLive = info.TimeToLive,
             PollIntervalMs = info.PollIntervalMs,
             StatusMessage = info.StatusMessage,
             ResultType = "complete",
@@ -1032,7 +1032,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
             TaskId = info.TaskId,
             CreatedAt = info.CreatedAt,
             LastUpdatedAt = info.LastUpdatedAt,
-            TtlMs = info.TtlMs,
+            TimeToLive = info.TimeToLive,
             PollIntervalMs = info.PollIntervalMs,
             StatusMessage = info.StatusMessage,
             Result = info.Result ?? throw new InvalidOperationException($"Task '{info.TaskId}' is completed but has no result."),
@@ -1043,7 +1043,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
             TaskId = info.TaskId,
             CreatedAt = info.CreatedAt,
             LastUpdatedAt = info.LastUpdatedAt,
-            TtlMs = info.TtlMs,
+            TimeToLive = info.TimeToLive,
             PollIntervalMs = info.PollIntervalMs,
             StatusMessage = info.StatusMessage,
             Error = info.Error ?? throw new InvalidOperationException($"Task '{info.TaskId}' is failed but has no error."),
@@ -1054,7 +1054,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
             TaskId = info.TaskId,
             CreatedAt = info.CreatedAt,
             LastUpdatedAt = info.LastUpdatedAt,
-            TtlMs = info.TtlMs,
+            TimeToLive = info.TimeToLive,
             PollIntervalMs = info.PollIntervalMs,
             StatusMessage = info.StatusMessage,
             ResultType = "complete",
@@ -1064,7 +1064,7 @@ await originalListToolsHandler(request, cancellationToken).ConfigureAwait(false)
             TaskId = info.TaskId,
             CreatedAt = info.CreatedAt,
             LastUpdatedAt = info.LastUpdatedAt,
-            TtlMs = info.TtlMs,
+            TimeToLive = info.TimeToLive,
             PollIntervalMs = info.PollIntervalMs,
             StatusMessage = info.StatusMessage,
             // McpTaskInfo.InputRequests is IReadOnlyDictionary (covers immutable store
diff --git a/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs b/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs
index ab71d6505..87fa8ef1c 100644
--- a/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs
+++ b/src/ModelContextProtocol.Core/Server/McpTaskInfo.cs
@@ -20,7 +20,7 @@ public sealed record McpTaskInfo(
     McpTaskStatus Status,
     DateTimeOffset CreatedAt,
     DateTimeOffset LastUpdatedAt,
-    long? TtlMs = null,
+    TimeSpan? TimeToLive = null,
     long? PollIntervalMs = null,
     string? StatusMessage = null,
     JsonElement? Result = null,
diff --git a/tests/ModelContextProtocol.Tests/Protocol/TaskSerializationTests.cs b/tests/ModelContextProtocol.Tests/Protocol/TaskSerializationTests.cs
index 556403add..86acc57f6 100644
--- a/tests/ModelContextProtocol.Tests/Protocol/TaskSerializationTests.cs
+++ b/tests/ModelContextProtocol.Tests/Protocol/TaskSerializationTests.cs
@@ -21,7 +21,7 @@ public static void CreateTaskResult_SerializationRoundTrip_PreservesAllPropertie
             StatusMessage = "Processing...",
             CreatedAt = new DateTimeOffset(2025, 6, 1, 12, 0, 0, TimeSpan.Zero),
             LastUpdatedAt = new DateTimeOffset(2025, 6, 1, 12, 5, 0, TimeSpan.Zero),
-            TtlMs = 3600000,
+            TimeToLive = TimeSpan.FromHours(1),
             PollIntervalMs = 5000,
             ResultType = "task",
             Meta = new JsonObject { ["key"] = "value" }
@@ -36,7 +36,7 @@ public static void CreateTaskResult_SerializationRoundTrip_PreservesAllPropertie
         Assert.Equal("Processing...", deserialized.StatusMessage);
         Assert.Equal(original.CreatedAt, deserialized.CreatedAt);
         Assert.Equal(original.LastUpdatedAt, deserialized.LastUpdatedAt);
-        Assert.Equal(3600000, deserialized.TtlMs);
+        Assert.Equal(TimeSpan.FromHours(1), deserialized.TimeToLive);
         Assert.Equal(5000, deserialized.PollIntervalMs);
         Assert.Equal("task", deserialized.ResultType);
         Assert.NotNull(deserialized.Meta);
@@ -52,7 +52,7 @@ public static void CreateTaskResult_UsesCorrectWireFieldNames()
             Status = McpTaskStatus.Working,
             CreatedAt = DateTimeOffset.UtcNow,
             LastUpdatedAt = DateTimeOffset.UtcNow,
-            TtlMs = 60000,
+            TimeToLive = TimeSpan.FromMinutes(1),
             PollIntervalMs = 1000,
             ResultType = "task",
         };
diff --git a/tests/ModelContextProtocol.Tests/Server/InMemoryMcpTaskStoreTests.cs b/tests/ModelContextProtocol.Tests/Server/InMemoryMcpTaskStoreTests.cs
index 7c87786eb..83afbfe23 100644
--- a/tests/ModelContextProtocol.Tests/Server/InMemoryMcpTaskStoreTests.cs
+++ b/tests/ModelContextProtocol.Tests/Server/InMemoryMcpTaskStoreTests.cs
@@ -55,13 +55,13 @@ public async Task CreateTaskAsync_UsesDefaultPollInterval()
     }
 
     [Fact]
-    public async Task CreateTaskAsync_UsesDefaultTtl()
+    public async Task CreateTaskAsync_UsesDefaultTimeToLive()
     {
-        var store = new InMemoryMcpTaskStore { DefaultTtlMs = 30000 };
+        var store = new InMemoryMcpTaskStore { DefaultTimeToLive = TimeSpan.FromSeconds(30) };
 
         var result = await store.CreateTaskAsync(CT);
 
-        Assert.Equal(30000, result.TtlMs);
+        Assert.Equal(TimeSpan.FromSeconds(30), result.TimeToLive);
     }
 
     [Fact]
diff --git a/tests/ModelContextProtocol.Tests/Server/TaskCancellationIntegrationTests.cs b/tests/ModelContextProtocol.Tests/Server/TaskCancellationIntegrationTests.cs
index 1b424d002..0e8693353 100644
--- a/tests/ModelContextProtocol.Tests/Server/TaskCancellationIntegrationTests.cs
+++ b/tests/ModelContextProtocol.Tests/Server/TaskCancellationIntegrationTests.cs
@@ -34,7 +34,7 @@ protected override void ConfigureServices(ServiceCollection services, IMcpServer
             options.TaskStore = new InMemoryMcpTaskStore
             {
                 DefaultPollIntervalMs = 50,
-                DefaultTtlMs = 5000,
+                DefaultTimeToLive = TimeSpan.FromSeconds(5),
             };
         });