diff --git a/CHANGELOG.md b/CHANGELOG.md
index 41e651319..fe2eab549 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,9 @@
 - Bump Native SDK from v0.14.0 to v0.14.2 ([#2685](https://github.com/getsentry/sentry-unity/pull/2685))
   - [changelog](https://github.com/getsentry/sentry-native/blob/master/CHANGELOG.md#0142)
   - [diff](https://github.com/getsentry/sentry-native/compare/0.14.0...0.14.2)
+- Bump .NET SDK from v6.6.0-1-g4a85500a to v6.6.0 ([#2698](https://github.com/getsentry/sentry-unity/pull/2698))
+  - [changelog](https://github.com/getsentry/sentry-dotnet/blob/main/CHANGELOG.md#660)
+  - [diff](https://github.com/getsentry/sentry-dotnet/compare/6.6.0-1-g4a85500a...6.6.0)
 
 ## 4.3.1
 
diff --git a/src/Sentry.Unity/Integrations/UnityScopeIntegration.cs b/src/Sentry.Unity/Integrations/UnityScopeIntegration.cs
index 84d771261..23c598bfb 100644
--- a/src/Sentry.Unity/Integrations/UnityScopeIntegration.cs
+++ b/src/Sentry.Unity/Integrations/UnityScopeIntegration.cs
@@ -159,17 +159,19 @@ private void PopulateUnity(Protocol.Unity unity)
 
     private void PopulateUser(Scope scope)
     {
-        if (scope.User.Id is not null)
+        // The .NET SDK pre-sets User.Id from its own InstallationId on the root scope in global
+        // mode. On mobile we want the native SDK's installation id so managed events and native
+        // crashes share a user identity — overwrite unconditionally when DefaultUserId is set.
+        if (_options.DefaultUserId is not null)
         {
-            return;
+            scope.User.Id = _options.DefaultUserId;
         }
 
-        // Only set the native installation ID here. The .NET SDK's Enricher handles
-        // the fallback to InstallationId after the HasUser() check, which allows
-        // IsEnvironmentUser/SendDefaultPii to set the Username first.
-        if (_options.DefaultUserId is not null)
+        // Enricher only applies Environment.UserName when the scope user has no data yet — and
+        // the pre-set User.Id above trips that gate. Apply it here so IsEnvironmentUser is honored.
+        if (scope.User.Username is null && _options.SendDefaultPii && _options.IsEnvironmentUser)
         {
-            scope.User.Id = _options.DefaultUserId;
+            scope.User.Username = Environment.UserName;
         }
     }
 }
diff --git a/src/sentry-dotnet b/src/sentry-dotnet
index 608fc74c4..0140be0a3 160000
--- a/src/sentry-dotnet
+++ b/src/sentry-dotnet
@@ -1 +1 @@
-Subproject commit 608fc74c4d40fef185473a9a329ae56aa8e0d978
+Subproject commit 0140be0a3b98ee01ff53097a5289bc6e7b703957
diff --git a/test/Sentry.Unity.Tests/UnityEventScopeTests.cs b/test/Sentry.Unity.Tests/UnityEventScopeTests.cs
index 6f756e3e4..2bf8103d5 100644
--- a/test/Sentry.Unity.Tests/UnityEventScopeTests.cs
+++ b/test/Sentry.Unity.Tests/UnityEventScopeTests.cs
@@ -343,19 +343,21 @@ public void UserId_SetIfEmpty()
     }
 
     [Test]
-    public void UserId_UnchangedIfNonEmpty()
+    public void UserId_DefaultUserIdOverwritesPreExisting()
     {
-        // arrange
-        var options = new SentryUnityOptions(application: _testApplication) { DefaultUserId = "foo" };
+        // arrange - simulates the .NET SDK's GlobalRootScopeIntegration pre-setting User.Id
+        // before UnityScopeIntegration runs. Unity's native installation id (DefaultUserId)
+        // must win so managed events and native crashes share the same User.Id.
+        var options = new SentryUnityOptions(application: _testApplication) { DefaultUserId = "native-id" };
         var sut = new UnityScopeUpdater(options, _testApplication);
         var scope = new Scope(options);
-        scope.User.Id = "bar";
+        scope.User.Id = "dotnet-installation-id";
 
         // act
         sut.ConfigureScope(scope);
 
         // assert
-        Assert.AreEqual(scope.User.Id, "bar");
+        Assert.AreEqual("native-id", scope.User.Id);
     }
 
     [Test]
@@ -395,17 +397,19 @@ public void UserId_ScopeSync_TriggeredWhenUserIdSet()
     }
 
     [Test]
-    public void UserId_ScopeSync_NotTriggeredWhenUserAlreadySet()
+    public void UserId_ScopeSync_TriggeredEvenWhenUserAlreadySet()
     {
-        // arrange - User.Id already set, PopulateUser should early-return
-        var options = new SentryUnityOptions(application: _testApplication) { DefaultUserId = "should-not-sync" };
+        // arrange - simulates the .NET SDK pre-setting User.Id before UnityScopeIntegration runs.
+        // PopulateUser must still overwrite with DefaultUserId so the native SDK receives the
+        // native installation id via the scope observer.
+        var options = new SentryUnityOptions(application: _testApplication) { DefaultUserId = "native-id" };
         var observer = new TestScopeObserver(options);
         options.ScopeObserver = observer;
         options.EnableScopeSync = true;
 
         var sut = new UnityScopeUpdater(options, _testApplication);
         var scope = new Scope(options);
-        scope.User.Id = "already-set";
+        scope.User.Id = "dotnet-installation-id";
 
         // Reset observer after the initial scope.User.Id set above triggered it
         observer.LastUser = null;
@@ -413,8 +417,9 @@ public void UserId_ScopeSync_NotTriggeredWhenUserAlreadySet()
         // act
         sut.ConfigureScope(scope);
 
-        // assert - PopulateUser should not have set a new user
-        Assert.IsNull(observer.LastUser, "ScopeObserver.SetUser should not be called when User.Id is already set");
+        // assert - PopulateUser overwrote and synced the native id
+        Assert.IsNotNull(observer.LastUser, "ScopeObserver.SetUser should be called when DefaultUserId is set");
+        Assert.AreEqual("native-id", observer.LastUser!.Id);
     }
 
     [Test]