diff --git a/src/cascadia/WindowsTerminal/WindowEmperor.cpp b/src/cascadia/WindowsTerminal/WindowEmperor.cpp
index 07e96fcc2e5..55244118c9d 100644
--- a/src/cascadia/WindowsTerminal/WindowEmperor.cpp
+++ b/src/cascadia/WindowsTerminal/WindowEmperor.cpp
@@ -315,16 +315,29 @@ AppHost* WindowEmperor::_mostRecentWindow() const noexcept
 
 void WindowEmperor::HandleCommandlineArgs(int nCmdShow)
 {
+    // When running without package identity, set an explicit AppUserModelID so
+    // that toast notifications (and other shell features like taskbar grouping)
+    // work correctly. We include...
+    // - a hash of the executable path
+    // - a hash of the user SID
+    // This prevents crosstalk between different portable/unpackaged installations.
+    // The same isolation strategy is used for the single-instance mutex below.
+    std::wstring unpackagedAumid;
+
     std::wstring windowClassName;
     windowClassName.reserve(64); // "Windows Terminal Preview Admin 0123456789012345 0123456789012345"
 #if defined(WT_BRANDING_RELEASE)
     windowClassName.append(L"Windows Terminal");
+    unpackagedAumid = L"Microsoft.WindowsTerminal";
 #elif defined(WT_BRANDING_PREVIEW)
     windowClassName.append(L"Windows Terminal Preview");
+    unpackagedAumid = L"Microsoft.WindowsTerminalPreview";
 #elif defined(WT_BRANDING_CANARY)
     windowClassName.append(L"Windows Terminal Canary");
+    unpackagedAumid = L"Microsoft.WindowsTerminalCanary";
 #else
     windowClassName.append(L"Windows Terminal Dev");
+    unpackagedAumid = L"WindowsTerminalDev";
 #endif
     if (Utils::IsRunningElevated())
     {
@@ -336,8 +349,10 @@ void WindowEmperor::HandleCommandlineArgs(int nCmdShow)
         const auto hash = til::hash(path);
 #ifdef _WIN64
         fmt::format_to(std::back_inserter(windowClassName), FMT_COMPILE(L" {:016x}"), hash);
+        fmt::format_to(std::back_inserter(unpackagedAumid), FMT_COMPILE(L".{:016x}"), hash);
 #else
         fmt::format_to(std::back_inserter(windowClassName), FMT_COMPILE(L" {:08x}"), hash);
+        fmt::format_to(std::back_inserter(unpackagedAumid), FMT_COMPILE(L".{:08x}"), hash);
 #endif
     }
 
@@ -351,6 +366,15 @@ void WindowEmperor::HandleCommandlineArgs(int nCmdShow)
 #else
         fmt::format_to(std::back_inserter(windowClassName), FMT_COMPILE(L" {:08x}"), hash);
 #endif
+        if (!IsPackaged())
+        {
+#ifdef _WIN64
+            fmt::format_to(std::back_inserter(unpackagedAumid), FMT_COMPILE(L".{:016x}"), hash);
+#else
+            fmt::format_to(std::back_inserter(unpackagedAumid), FMT_COMPILE(L".{:08x}"), hash);
+#endif
+            LOG_IF_FAILED(SetCurrentProcessExplicitAppUserModelID(unpackagedAumid.c_str()));
+        }
     }
 
     // Windows Terminal is a single-instance application. Either acquire ownership