diff --git a/src/ClaudeDo.Ui/ClaudeDo.Ui.csproj b/src/ClaudeDo.Ui/ClaudeDo.Ui.csproj
index dc83e5e..c296826 100644
--- a/src/ClaudeDo.Ui/ClaudeDo.Ui.csproj
+++ b/src/ClaudeDo.Ui/ClaudeDo.Ui.csproj
@@ -2,6 +2,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\ClaudeDo.Data\ClaudeDo.Data.csproj" />
+    <ProjectReference Include="..\ClaudeDo.Releases\ClaudeDo.Releases.csproj" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/ClaudeDo.Ui/Services/UpdateCheckService.cs b/src/ClaudeDo.Ui/Services/UpdateCheckService.cs
new file mode 100644
index 0000000..bd72759
--- /dev/null
+++ b/src/ClaudeDo.Ui/Services/UpdateCheckService.cs
@@ -0,0 +1,73 @@
+using ClaudeDo.Releases;
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ClaudeDo.Ui.Services;
+
+public enum UpdateCheckStatus
+{
+    NeverChecked,
+    CheckFailed,
+    UpToDate,
+    UpdateAvailable,
+}
+
+public sealed partial class UpdateCheckService : ObservableObject
+{
+    private readonly IReleaseClient _releases;
+
+    [ObservableProperty] private bool _isUpdateAvailable;
+    [ObservableProperty] private string? _latestVersion;
+    [ObservableProperty] private string _currentVersion;
+    [ObservableProperty] private bool _isChecking;
+    [ObservableProperty] private UpdateCheckStatus _lastCheckStatus = UpdateCheckStatus.NeverChecked;
+
+    public UpdateCheckService(IReleaseClient releases, string currentVersion)
+    {
+        _releases = releases;
+        _currentVersion = currentVersion;
+    }
+
+    public async Task CheckNowAsync(CancellationToken ct)
+    {
+        IsChecking = true;
+        try
+        {
+            GiteaRelease? rel;
+            try
+            {
+                rel = await _releases.GetLatestReleaseAsync(ct);
+            }
+            catch
+            {
+                LastCheckStatus = UpdateCheckStatus.CheckFailed;
+                IsUpdateAvailable = false;
+                return;
+            }
+
+            if (rel is null)
+            {
+                LastCheckStatus = UpdateCheckStatus.CheckFailed;
+                IsUpdateAvailable = false;
+                return;
+            }
+
+            var latest = (rel.TagName ?? "").TrimStart('v', 'V');
+            var cmp = VersionComparer.Compare(latest, CurrentVersion);
+            if (cmp.IsNewer)
+            {
+                LatestVersion = latest;
+                IsUpdateAvailable = true;
+                LastCheckStatus = UpdateCheckStatus.UpdateAvailable;
+            }
+            else
+            {
+                IsUpdateAvailable = false;
+                LastCheckStatus = UpdateCheckStatus.UpToDate;
+            }
+        }
+        finally
+        {
+            IsChecking = false;
+        }
+    }
+}
diff --git a/tests/ClaudeDo.Ui.Tests/Services/UpdateCheckServiceTests.cs b/tests/ClaudeDo.Ui.Tests/Services/UpdateCheckServiceTests.cs
new file mode 100644
index 0000000..77b5956
--- /dev/null
+++ b/tests/ClaudeDo.Ui.Tests/Services/UpdateCheckServiceTests.cs
@@ -0,0 +1,62 @@
+using System.Net.Http;
+using ClaudeDo.Releases;
+using ClaudeDo.Ui.Services;
+
+namespace ClaudeDo.Ui.Tests.Services;
+
+public class UpdateCheckServiceTests
+{
+    private sealed class FakeReleaseClient : IReleaseClient
+    {
+        public GiteaRelease? Release { get; set; }
+        public bool Throw { get; set; }
+
+        public Task<GiteaRelease?> GetLatestReleaseAsync(CancellationToken ct)
+        {
+            if (Throw) throw new HttpRequestException();
+            return Task.FromResult(Release);
+        }
+
+        public Task DownloadAsync(string url, string destPath, IProgress<long> progress, CancellationToken ct)
+            => throw new NotSupportedException();
+    }
+
+    [Fact]
+    public async Task Check_NewerRelease_SetsUpdateAvailable()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.3.0", "r", new[] { new ReleaseAsset("ClaudeDo-0.3.0-win-x64.zip", "u", 1) }),
+        },
+        currentVersion: "0.1.0");
+
+        await svc.CheckNowAsync(CancellationToken.None);
+
+        Assert.Equal(UpdateCheckStatus.UpdateAvailable, svc.LastCheckStatus);
+        Assert.True(svc.IsUpdateAvailable);
+        Assert.Equal("0.3.0", svc.LatestVersion);
+    }
+
+    [Fact]
+    public async Task Check_SameRelease_SetsUpToDate()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.1.0", "r", new[] { new ReleaseAsset("ClaudeDo-0.1.0-win-x64.zip", "u", 1) }),
+        },
+        currentVersion: "0.1.0");
+
+        await svc.CheckNowAsync(CancellationToken.None);
+
+        Assert.Equal(UpdateCheckStatus.UpToDate, svc.LastCheckStatus);
+        Assert.False(svc.IsUpdateAvailable);
+    }
+
+    [Fact]
+    public async Task Check_NetworkError_SetsCheckFailedButDoesNotThrow()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient { Throw = true }, "0.1.0");
+        await svc.CheckNowAsync(CancellationToken.None);
+        Assert.Equal(UpdateCheckStatus.CheckFailed, svc.LastCheckStatus);
+    }
+}