This is a stable release of C#/WinRT focused on bringing .NET AOT support and improved trimming support to both the runtime and generated projections. This version requires the following Windows SDK projection package from below or later which can be consumed by setting the below property in your C# project file or by updating to September's .NET SDK servicing build once available.

More details on the effect of these improvements and known issues can be found here: https://github.com/microsoft/CsWinRT/blob/2.1.1.240807.2/docs/aot-trimming.md

C#/WinRT package:
https://www.nuget.org/packages/Microsoft.Windows.CsWinRT/2.1.1

.NET Windows SDK targeting packages for .NET 6:

<WindowsSdkPackageVersion>10.0.xxxxx.38</WindowsSdkPackageVersion>

https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.26100.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.22621.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.22000.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.20348.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.19041.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.18362.38
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.17763.38

.NET Windows SDK targeting packages for .NET 8:

<WindowsSdkPackageVersion>10.0.xxxxx.41</WindowsSdkPackageVersion>

https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.26100.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.22621.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.22000.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.20348.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.19041.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.18362.41
https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref/10.0.17763.41

As part of these Windows SDK projection builds, there were several types in the Windows.UI namespace that were moved from the WinUI projection to the Windows SDK projection to avoid long-term type conflict issues. Most of them have Microsoft.UI versions of them which are used in WinUI scenarios. There are a couple used in WinUI scenarios such as TextDecorations, BindableAttribute, and ContentPropertyAttribute. If you do use one of them and run into a type conflict issue between Microsoft.WinUI and Microsoft.Windows.SDK.NET, it can be resolved by moving to Microsoft.WindowsAppSDK 1.6 or by using the WindowsSdkPackageVersion property to use an older version of the Windows SDK projection such as .34 if you can't move forward your Microsoft.WindowsAppSDK version yet.

Thank you again to Dongle (@dongle-the-gadget), 高怡飞 (@Gaoyifei1011), Steve (@hez2010), Jevan Saks (@jevansaks), Jeremy Price (@Jeremy-Price), Johan Laanstra (@jlaanstra), Jeremy Koritzinsky (@jkoritzinsky), Sergio Pedri (@Sergio0694) for your community contributions to this significant release and for everyone who reported issues with the previews.

What's Changed

• Initial changes to make vtable generation trimming safe for AOT by Manodasan Wignarajah (@manodasanW) in #1352
• Update staging with latest by Manodasan Wignarajah (@manodasanW) in #1361
• Revert "Update staging with latest" by Manodasan Wignarajah (@manodasanW) in #1362
• Update staging again with latest without squash by Manodasan Wignarajah (@manodasanW) in #1363
• Update staging with latest by Manodasan Wignarajah (@manodasanW) in #1374
• Remove the need for GuidGenerator/IIDOptimizer for all ABI interfaces. by Johan Laanstra (@jlaanstra) in #1360
• Merge master to staging by Manodasan Wignarajah (@manodasanW) in #1378
• Use Marshal.AddRef/Release/QueryInterface. by Johan Laanstra (@jlaanstra) in #1379
• Run benchmarks against .NET 6 dll. by Johan Laanstra (@jlaanstra) in #1382
• Cache StringBuilder per thread and remove Lazy from GetRuntimeClassName. by Johan Laanstra (@jlaanstra) in #1381
• Addressing issues with generics on AOT by Manodasan Wignarajah (@manodasanW) in #1377
• Skip interfaces not publicly accessible in authoring scenarios by Sergio Pedri (@Sergio0694) in #1394
• Add MarshalString.FromAbiUnsafe API by Sergio Pedri (@Sergio0694) in #1400
• Use hardcoded IIDs for all well known IReferenceArray types by Sergio Pedri (@Sergio0694) in #1402
• Small tweaks to Marshaler's static cctor by Sergio Pedri (@Sergio0694) in #1413
• Fix issue with properties implemented across multiple static interfaces by Manodasan Wignarajah (@manodasanW) in #1415
• Move generic delegates vtable generation into projections by Manodasan Wignarajah (@manodasanW) in #1411
• Minor trimming optimizations for authoring by Sergio Pedri (@Sergio0694) in #1396
• Allow dropping native host for NativeAOT WinRT components by Sergio Pedri (@Sergio0694) in #1395
• Fixing issues discovered during validation by Manodasan Wignarajah (@manodasanW) in #1436
• Skip unnecessary lookup in EventRegistrationTokenTable by Sergio Pedri (@Sergio0694) in #1440
• Optimize EventRegistrationTokenTable removal by Sergio Pedri (@Sergio0694) in #1445
• Add support for feature switches, add option to disable dynamic objects support by Sergio Pedri (@Sergio0694) in #1435
• Remove LINQ expression dependencies on NativeAOT by Sergio Pedri (@Sergio0694) in #1429
• Rewrite event registration token logic to improve performance, trimming by Sergio Pedri (@Sergio0694) in #1448
• Rewrite MarshalGeneric to minimize binary size on NativeAOT by Sergio Pedri (@Sergio0694) in #1437
• Omit non public methods from preserved metadata by Sergio Pedri (@Sergio0694) in #1442
• Fix IL2091 warnings in generated activation factories by Sergio Pedri (@Sergio0694) in #1449
• Improve Marshaler trimming for blittable types by Sergio Pedri (@Sergio0694) in #1455
• Drop [DynamicallyAccessedMembers] from Marshaler.AbiType by Sergio Pedri (@Sergio0694) in #1461
• Remove unnecessary lambda expression stubs by Sergio Pedri (@Sergio0694) in #1462
• Make marshalling 'System.Type' AOT-safe by Sergio Pedri (@Sergio0694) in #1459
• Stop using ThreadLocal, use [ThreadStatic] by Sergio Pedri (@Sergio0694) in #1460
• Move EventRegistrationTokenTable to WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1456
• Drop all delegates and closures in MarshalInterface on NAOT by Sergio Pedri (@Sergio0694) in #1450
• Expose api's for Context on ObjectReference. by Johan Laanstra (@jlaanstra) in #1466
• Reduce enum stubs codegen with NativeAOT by Sergio Pedri (@Sergio0694) in #1441
• Move ActivationFactory into WinRT.Runtime.dll by Johan Laanstra (@jlaanstra) in #1390
• Reduce binary size in agile reference context cache by Sergio Pedri (@Sergio0694) in #1468
• Optimize ContextCallback on modern .NET by Sergio Pedri (@Sergio0694) in #1464
• Seal IObjectReference.TryAs method by Sergio Pedri (@Sergio0694) in #1454
• Move private delegate extensions to WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1457
• Make exported DllGetActivationFactory zero-alloc (take 2) by Sergio Pedri (@Sergio0694) in #1401
• Remove generated VftblPtr type by Sergio Pedri (@Sergio0694) in #1397
• Cherry-pick #1380 (remove resurrect logic) by Sergio Pedri (@Sergio0694) in #1469
• Trim out more legacy projections fallback paths by Sergio Pedri (@Sergio0694) in #1443
• Skip unnecessary method group delegate cache by Sergio Pedri (@Sergio0694) in #1470
• Remove object field and allocation from ObjectReference by Sergio Pedri (@Sergio0694) in #1458
• Stop preserving interfaces from MarshalInspectable by Sergio Pedri (@Sergio0694) in #1452
• Remove Lazy uses on NativeAOT by Sergio Pedri (@Sergio0694) in #1473
• Move all Platform APIs to WinRT.Runtime, remove leftover ones by Sergio Pedri (@Sergio0694) in #1472
• Use typeof(DllModule).Assembly for faster resolution by Sergio Pedri (@Sergio0694) in #1475
• Support nested types in AOT generator by Sergio Pedri (@Sergio0694) in #1479
• Hard-code the numeric scalar types in CoerceValue and simplify enum marshalling to remove any usage of Convert.ChangeType. by Jeremy Koritzinsky (@jkoritzinsky) in #1487
• Remove/move internal vftbl types by Sergio Pedri (@Sergio0694) in #1493
• Move DynamicInvokeAbi into WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1490
• Move IActivationFactoryMethods.ActivateInstance into WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1489
• Add 'EnableDefaultCustomTypeMappings' switch by Sergio Pedri (@Sergio0694) in #1483
• Remove ComponentActivationFactory types by Sergio Pedri (@Sergio0694) in #1491
• Remove almost all LINQ uses by Sergio Pedri (@Sergio0694) in #1486
• Add net8.0 as target in help by Dongle (@dongle-the-gadget) in #1498
• Move InterfaceIIDs to WinRT.Runtime, rename it to IID by Sergio Pedri (@Sergio0694) in #1494
• Fix TFM check in generated activation factories by Sergio Pedri (@Sergio0694) in #1484
• Minor performance improvements to MarshalBlittable by Sergio Pedri (@Sergio0694) in #1502
• Simplify and optimize exception helpers by Sergio Pedri (@Sergio0694) in #1495
• Add [WinRTImplementationTypeRcwFactory] type by Sergio Pedri (@Sergio0694) in #1505
• Suppress incorrect CA2257 warnings by Sergio Pedri (@Sergio0694) in #1509
• Fix some warnings by Sergio Pedri (@Sergio0694) in #1506
• Remove [ObjectReferenceWrapper] on .NET 6+ by Sergio Pedri (@Sergio0694) in #1507
• Allow authoring scenarios to make use of abstract classes in their implementation by Manodasan Wignarajah (@manodasanW) in #1512
• Remove managed vtable support on .NET 6+ by Sergio Pedri (@Sergio0694) in #1504
• Fix, obsolete and hide AsType() on .NET 6 by Sergio Pedri (@Sergio0694) in #1513
• Remove [Serializable] support from exceptions by Sergio Pedri (@Sergio0694) in #1453
• Merge master to staging branch by Manodasan Wignarajah (@manodasanW) in #1516
• Fix issue where RuntimeConfiguration defaults are not used by Manodasan Wignarajah (@manodasanW) in #1530
• Obsolete Marshaler.RefAbiType on .NET 6+ by Sergio Pedri (@Sergio0694) in #1520
• Enable IsAotCompatible for CsWinRT, fix all AOT warnings by Sergio Pedri (@Sergio0694) in #1463
• Suppress useless IL2080 warnings in fallback paths by Sergio Pedri (@Sergio0694) in #1515
• Add DataTransferManger interop APIs by 高怡飞 (@Gaoyifei1011) in #1528
• Fix bug in the AsStream extensions where the Length isn't properly updated on the IBuffer. by Johan Laanstra (@jlaanstra) in #1536
• Add ActivationHandler to match the C++/WinRT winrt_activation_handler. by Johan Laanstra (@jlaanstra) in #1532
• Add additional tests and benchmarks for async. by Johan Laanstra (@jlaanstra) in #1538
• Fix ShowShareUIForWindow method name. by Dongle (@dongle-the-gadget) in #1540
• Make AsyncInfoToTaskBridge lock free and more responsive to cancellation. by Johan Laanstra (@jlaanstra) in #1539
• Optimize AsTask when the underlying IAsyncOperation is wrapping a task. by Johan Laanstra (@jlaanstra) in #1537
• Move EventSource and associated types to WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1497
• Addressed a couple missed out on unmanaged function pointers by Manodasan Wignarajah (@manodasanW) in #1549
• Stop rooting nested types for helper types by Sergio Pedri (@Sergio0694) in #1521
• Use supported ILC patterns in projections by Sergio Pedri (@Sergio0694) in #1471
• Fix remaining scenarios still calling FindVftblType by Manodasan Wignarajah (@manodasanW) in #1545
• Merge master to staging branch by Manodasan Wignarajah (@manodasanW) in #1552
• Adding diagnostics and code fix for adding partial keyword by Manodasan Wignarajah (@manodasanW) in #1554
• Stop generating explicit interface implementations when not needed. by Johan Laanstra (@jlaanstra) in #1553
• Add overloads for CopyTo for Span. by Johan Laanstra (@jlaanstra) in #1541
• Use MethodInvoker in MarshalGenericFallback by Sergio Pedri (@Sergio0694) in #1561
• Add RcwReflectionFallbackGenerator type by Sergio Pedri (@Sergio0694) in #1555
• Fixing various crashes discovered with latest builds and removing vftbl by Manodasan Wignarajah (@manodasanW) in #1560
• Strong name sign source generator by Manodasan Wignarajah (@manodasanW) in #1558
• Add 'CsWinRTEnableICustomPropertyProviderSupport' feature switch by Sergio Pedri (@Sergio0694) in #1565
• Fix more warnings in WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1557
• Add AsInterface support for generated COM interfaces. by Dongle (@dongle-the-gadget) in #1534
• Fix trim warnings in 'AdaptiveFromAbiHelper' by Sergio Pedri (@Sergio0694) in #1566
• Fix an incorrect IL3050 warning suppression for ILC by Sergio Pedri (@Sergio0694) in #1568
• Add WinRTRuntimeClassName attribute for use in scenarios where we previously used interface name by Manodasan Wignarajah (@manodasanW) in #1573
• Add 3 missing trimming suppressions by Sergio Pedri (@Sergio0694) in #1574
• Add 'CsWinRTEnableIReferenceSupport' feature switch by Sergio Pedri (@Sergio0694) in #1575
• Disable runtime marshalling for the CsWinRT repo. by Johan Laanstra (@jlaanstra) in #1431
• Add missed test changes from previous PR by Manodasan Wignarajah (@manodasanW) in #1579
• Don't cache 'RegisterTypeRuntimeClassNameLookup' by Sergio Pedri (@Sergio0694) in #1586
• Fix CCW for boxing scenarios of generic types by Manodasan Wignarajah (@manodasanW) in #1585
• Add 'CsWinRTEnableIDynamicInterfaceCastableSupport' feature switch by Sergio Pedri (@Sergio0694) in #1583
• Add convenience methods directly on IAsyncAction/Operation to facilitate future optimizations and custom Awaiter/Task types. by Johan Laanstra (@jlaanstra) in #1580
• Remove more closures in lambda expressions by Sergio Pedri (@Sergio0694) in #1588
• Fix IL2087 trim warning in 'ObjectReferenceWithContext' by Sergio Pedri (@Sergio0694) in #1577
• Pass more explicit IIDs in more places by Sergio Pedri (@Sergio0694) in #1594
• Set 'TreatWarningsAsErrors' almost everywhere by Sergio Pedri (@Sergio0694) in #1592
• Seal and tweak 'IWinRTObject' members by Sergio Pedri (@Sergio0694) in #1591
• Add 'CsWinRTRcwFactoryFallbackGeneratorForceOptOut' property by Sergio Pedri (@Sergio0694) in #1567
• Pass IID for 'IBufferByteAccess.FromAbi' by Sergio Pedri (@Sergio0694) in #1596
• Small optimization in 'GetAuthoringMetadataType' by Sergio Pedri (@Sergio0694) in #1599
• Obsolete reflection-based 'ObjectReference' APIs by Sergio Pedri (@Sergio0694) in #1595
• Remove 'Marshal.StructureToPtr' calls by Sergio Pedri (@Sergio0694) in #1600
• Strip generated authoring metadata types by Sergio Pedri (@Sergio0694) in #1598
• Reduce 'ObjectReference' generic instantiations in WinRT.Runtime by Sergio Pedri (@Sergio0694) in #1597
• Remove leftover implicit operators on .NET target by Sergio Pedri (@Sergio0694) in #1601
• Add WindowsRuntimeMarshal.TryGetDataUnsafe and use it in various places. by Johan Laanstra (@jlaanstra) in #1556
• Add missing check for 'IReference' support by Sergio Pedri (@Sergio0694) in #1603
• Avoid closure in 'CreateReferenceCachingFactory' by Sergio Pedri (@Sergio0694) in #1605
• Fixing couple reported issues by Manodasan Wignarajah (@manodasanW) in #1604
• Optimize 'IGlobalInterfaceTable' on .NET by Sergio Pedri (@Sergio0694) in #1607
• Add WindowsRuntimeMarshal.TryGetArray(IBuffer, out ArraySegment) by Johan Laanstra (@jlaanstra) in #1542
• Add missing check for nullable delegates by Sergio Pedri (@Sergio0694) in #1608
• Merge master to staging/AOT by Manodasan Wignarajah (@manodasanW) in #1614
• Fixing issues from GetObjectReferenceFromInterface change by Manodasan Wignarajah (@manodasanW) in #1616
• Update baseline in staging/AOT by Manodasan Wignarajah (@manodasanW) in #1618
• Fix edge cases with .NET Standard embedded support by Manodasan Wignarajah (@manodasanW) in #1621
• Adding known issues for AOT staging branch by Manodasan Wignarajah (@manodasanW) in #1627
• Don't cache 'RegisterTypeComInterfaceEntriesLookup' by Sergio Pedri (@Sergio0694) in #1622
• Minor changes to IIDOptimizer and AOTOptimizer by Manodasan Wignarajah (@manodasanW) in #1626
• Fix marshaling in AOT source generator by Manodasan Wignarajah (@manodasanW) in #1628
• Unify all IIDs into 'IID' type by Sergio Pedri (@Sergio0694) in #1620
• Add missing 'readonly' modifiers to static (P)IID fields by Sergio Pedri (@Sergio0694) in #1612
• Trim 'ABI.System.EventHandler' when not needed by Sergio Pedri (@Sergio0694) in #1619
• Fix .NET Standard authoring support by Manodasan Wignarajah (@manodasanW) in #1632
• Fix 'CsWinRTIncludes' check in .targets file by Sergio Pedri (@Sergio0694) in #1625
• WUX/MUX prototype by Jeremy Koritzinsky (@jkoritzinsky) in #1421
• Merge master into staging branch by Manodasan Wignarajah (@manodasanW) in #1652
• Add 'CsWinRTMergeReferencedActivationFactories' option by Sergio Pedri (@Sergio0694) in #1637
• Add WUX 'DispatcherQueueSynchronizationContext' type by Sergio Pedri (@Sergio0694) in #1647
• Fixing various AOT bugs by Manodasan Wignarajah (@manodasanW) in #1648
• Fix boxing of types by Manodasan Wignarajah (@manodasanW) in #1646
• Fix invalid cast exception with stream APIs and make code fixer emit diagnostics as warnings by Manodasan Wignarajah (@manodasanW) in #1654
• Fix IDIC casts to invalid WinRT interfaces by Manodasan Wignarajah (@manodasanW) in #1659
• Fix incorrect AOT runtime feature check by Sergio Pedri (@Sergio0694) in #1665
• Skip checking COM objects on AOT by Sergio Pedri (@Sergio0694) in #1662
• Add missing 'readonly' modifiers by Sergio Pedri (@Sergio0694) in #1664
• Improve codegen for merged activation factories by Sergio Pedri (@Sergio0694) in #1660
• Simplify WUX feature switch property by Sergio Pedri (@Sergio0694) in #1658
• Add -public_exclusiveto flag to enable implementing exclusiveto interfaces in consuming projects by Jevan Saks (@jevansaks) in #1670
• Add 'TryGetDataUnsafe' overload for 'IMemoryBufferReference' by Sergio Pedri (@Sergio0694) in #1673
• Fix IDIC casts throwing exceptions for is operator checks by Manodasan Wignarajah (@manodasanW) in #1676
• Fix class name mapping for WUX types by Sergio Pedri (@Sergio0694) in #1679
• Make ICustomPropertyProvider AOT safe by Manodasan Wignarajah (@manodasanW) in #1677
• Fix property initializers and derived ObservableCollection by Manodasan Wignarajah (@manodasanW) in #1686
• Fix merged component support in non-WinRT component projects by Sergio Pedri (@Sergio0694) in #1680
• Fix nullable scenarios when xaml asks for type and fix vtable for event handlers by Manodasan Wignarajah (@manodasanW) in #1684
• Remove redundant items in .targets by Sergio Pedri (@Sergio0694) in #1687
• Fix source generator for exception types and fix is operator by Manodasan Wignarajah (@manodasanW) in #1682
• Fix errors when consumers are using InternalsVisisbleTo by Manodasan Wignarajah (@manodasanW) in #1688
• Fix GetGuidSignature for event args by Manodasan Wignarajah (@manodasanW) in #1692
• Fix regression in IBindableIterator by Manodasan Wignarajah (@manodasanW) in #1690
• Rename BindableCustomProperty attribute to include Generated prefix by Manodasan Wignarajah (@manodasanW) in #1691
• Updating manifest which was forgotten when type was added by Manodasan Wignarajah (@manodasanW) in #1694
• Fix scenario where generic implementation type doesn't have type factory intialized by Manodasan Wignarajah (@manodasanW) in #1693
• Guard against potential null for RCW type by Manodasan Wignarajah (@manodasanW) in #1695
• Fix source link with mirror repos by Manodasan Wignarajah (@manodasanW) in #1699
• Make contracts internal when using embedded by Manodasan Wignarajah (@manodasanW) in #1698
• Merge master to staging/AOT branch by Manodasan Wignarajah (@manodasanW) in #1700
• Fix get type for nullable enums and fix WUX projections by Manodasan Wignarajah (@manodasanW) in #1701
• Add .NET 8 version to nuget package by Manodasan Wignarajah (@manodasanW) in #1704
• Allow projecting Windows.UI.ColorHelper type by Sergio Pedri (@Sergio0694) in #1706
• Add some more missing 'readonly' modifiers by Sergio Pedri (@Sergio0694) in #1707
• Add 'Windows.UI.Xaml.*' exception types by Sergio Pedri (@Sergio0694) in #1705
• Merge AOT changes to master by Manodasan Wignarajah (@manodasanW) in #1708
• Make generator compatible with older version of projections by Manodasan Wignarajah (@manodasanW) in #1710
• Fix diagnostic rule to be warning and not error by Manodasan Wignarajah (@manodasanW) in #1711

Full Changelog: 2.0.8.240703.1...2.1.1.240807.2