diff --git a/cppwinrt/main.cpp b/cppwinrt/main.cpp
index 1c6aadc36..1e39767c1 100644
--- a/cppwinrt/main.cpp
+++ b/cppwinrt/main.cpp
@@ -680,10 +680,6 @@ R"(  local               Local ^%WinDir^%\System32\WinMetadata folder
                     write_module_h();
                 }
                 write_base_h();
-                if (!settings.modules)
-                {
-                    ixx.flush_to_file(settings.output_folder + "winrt/winrt.ixx");
-                }
             }
 
             if (settings.component)
diff --git a/test/test_component/test_component.vcxproj b/test/test_component/test_component.vcxproj
index fcd32a79d..084ad0d40 100644
--- a/test/test_component/test_component.vcxproj
+++ b/test/test_component/test_component.vcxproj
@@ -383,7 +383,7 @@
   <ItemDefinitionGroup>
     <CustomBuildStep>
       <Command>
-      $(CppWinRTDir)cppwinrt -in local -out $(OutputPath) -verbose
+      $(CppWinRTDir)cppwinrt -in local -out $(OutputPath) -verbose -modules
       $(CppWinRTDir)cppwinrt -input $(OutputPath)test_component.winmd -comp "$(ProjectDir)Generated Files" -out "$(ProjectDir)Generated Files" -include test_component -ref sdk -verbose -prefix -opt -lib test -fastabi -overwrite -name test_component
       </Command>
       <Message>Projecting Windows and component metadata into $(OutputPath)</Message>
diff --git a/test/test_cpp20/array_span.cpp b/test/test_cpp20/array_span.cpp
index 69fd7aa36..dd27d6358 100644
--- a/test/test_cpp20/array_span.cpp
+++ b/test/test_cpp20/array_span.cpp
@@ -1,6 +1,10 @@
-#include "pch.h"
+#include <Windows.h>
 #include "catch.hpp"
-#include <array>
+
+import std;
+import Windows.Foundation;
+import Windows.Storage.Streams;
+import Windows.Data.Json;
 
 using namespace winrt;
 using namespace Windows::Foundation;
@@ -10,7 +14,7 @@ using namespace Windows::Data::Json;
 //
 // This is a helper to create a data reader for use in testing arrays.
 //
-static IAsyncOperation<IDataReader> CreateDataReader(std::initializer_list<byte> /*values*/)
+static IAsyncOperation<IDataReader> CreateDataReader(std::initializer_list<std::uint8_t> /*values*/)
 {
     InMemoryRandomAccessStream stream;
     DataWriter writer(stream);
@@ -32,8 +36,8 @@ TEST_CASE("array,DataReader,std::span")
 {
     auto reader = CreateDataReader({ 1, 2, 3 }).get();
 
-    std::array<byte, 3> a{};
-    std::span<byte> sp(a);
+    std::array<std::uint8_t, 3> a{};
+    std::span<std::uint8_t> sp(a);
     reader.ReadBytes(sp); // FillArray pattern
 
     REQUIRE(a.size() == 3);
@@ -49,7 +53,7 @@ TEST_CASE("array,DataReader,std::span,direct")
 {
     auto reader = CreateDataReader({ 1, 2, 3 }).get();
 
-    std::array<byte, 3> a{};
+    std::array<std::uint8_t, 3> a{};
     reader.ReadBytes(a); // FillArray pattern
 
     REQUIRE(a.size() == 3);
@@ -154,7 +158,7 @@ TEST_CASE("array_view,span,ctad")
 #define REQUIRE_DEDUCED_AS(T, ...) \
     static_assert(std::is_same_v<array_view<T>, decltype(array_view(__VA_ARGS__))>)
 
-    std::uint8_t a[] = {1, 2, 3};
+    std::uint8_t a[] = { 1, 2, 3 };
     std::span<std::uint8_t, 3> sp{ a };
 
     REQUIRE_DEDUCED_AS(std::uint8_t, sp);
diff --git a/test/test_cpp20/async.cpp b/test/test_cpp20/async.cpp
new file mode 100644
index 000000000..978825868
--- /dev/null
+++ b/test/test_cpp20/async.cpp
@@ -0,0 +1,92 @@
+#include <Windows.h>
+#include "catch.hpp"
+
+import std;
+import Windows.Foundation;
+
+using namespace winrt;
+using namespace Windows::Foundation;
+using namespace std::chrono_literals;
+
+namespace
+{
+    //
+    // Just some quick tests to make sure that coroutines compile and work with C++20 modules.
+    // Taken from async_throw in test
+    //
+    // TODO: make a new project for this
+
+    IAsyncAction Action()
+    {
+        co_await 10ms;
+        throw hresult_invalid_argument(L"Async");
+    }
+
+    IAsyncActionWithProgress<int> ActionWithProgress()
+    {
+        co_await 10ms;
+        throw hresult_invalid_argument(L"Async");
+    }
+
+    IAsyncOperation<int> Operation()
+    {
+        co_await 10ms;
+        throw hresult_invalid_argument(L"Async");
+        co_return 1;
+    }
+
+    IAsyncOperationWithProgress<int, int> OperationWithProgress()
+    {
+        co_await 10ms;
+        throw hresult_invalid_argument(L"Async");
+        co_return 1;
+    }
+
+    template <typename F>
+    void Check(F make)
+    {
+        try
+        {
+            make().get();
+            REQUIRE(false);
+        }
+        catch (hresult_invalid_argument const& e)
+        {
+            REQUIRE(e.message() == L"Async");
+        }
+
+        handle completed{ CreateEvent(nullptr, true, false, nullptr) };
+        auto async = make();
+
+        async.Completed([&](auto&& sender, AsyncStatus status)
+            {
+                REQUIRE(async == sender);
+                REQUIRE(status == AsyncStatus::Error);
+                SetEvent(completed.get());
+            });
+
+        REQUIRE(WaitForSingleObject(completed.get(), 1000) == WAIT_OBJECT_0);
+        REQUIRE(async.Status() == AsyncStatus::Error);
+
+        hresult_error e(async.ErrorCode(), take_ownership_from_abi);
+        REQUIRE(e.message() == L"Async");
+
+        try
+        {
+            async.GetResults();
+            REQUIRE(false);
+        }
+        catch (hresult_invalid_argument const& e)
+        {
+            REQUIRE(e.message() == L"Async");
+        }
+    }
+}
+
+TEST_CASE("async_throw")
+{
+    Check(Action);
+    Check(ActionWithProgress);
+    Check(Operation);
+    Check(OperationWithProgress);
+}
\ No newline at end of file
diff --git a/test/test_cpp20/await_completed.cpp b/test/test_cpp20/await_completed.cpp
index b1ba9e209..779f6d15c 100644
--- a/test/test_cpp20/await_completed.cpp
+++ b/test/test_cpp20/await_completed.cpp
@@ -1,4 +1,9 @@
-#include "pch.h"
+#include <intrin.h>
+
+#include "catch.hpp"
+
+import std;
+import Windows.Foundation;
 
 using namespace winrt;
 using namespace Windows::Foundation;
diff --git a/test/test_cpp20/clang_only.cpp b/test/test_cpp20/clang_only.cpp
index 45aa4b380..88b90d71b 100644
--- a/test/test_cpp20/clang_only.cpp
+++ b/test/test_cpp20/clang_only.cpp
@@ -1,4 +1,4 @@
-#include "pch.h"
+#include <winrt/Windows.Foundation.h>
 #include <winrt/Windows.Storage.Pickers.h>
 
 #ifdef __clang__
diff --git a/test/test_cpp20/custom_error.cpp b/test/test_cpp20/custom_error.cpp
index fbaf407f9..08f5c6eb9 100644
--- a/test/test_cpp20/custom_error.cpp
+++ b/test/test_cpp20/custom_error.cpp
@@ -1,4 +1,9 @@
-#include "pch.h"
+#include "catch.hpp"
+#include <Windows.h>
+
+import std;
+import winrt.base;
+import Windows.Foundation;
 
 using namespace winrt;
 using namespace Windows::Foundation;
@@ -35,12 +40,7 @@ namespace
     }
 }
 
-#if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION < 170000
-// <source_location> not available in libc++ before LLVM 16
-TEST_CASE("custom_error_logger_on_throw", "[!shouldfail]")
-#else
 TEST_CASE("custom_error_logger_on_throw")
-#endif
 {
     // Set up global handler
     REQUIRE(!s_loggerCalled);
@@ -80,12 +80,7 @@ void HresultOnLine80(Args... args)
     winrt::hresult_canceled(std::forward<Args>(args)...);
 }
 
-#if defined(_LIBCPP_VERSION) && _LIBCPP_VERSION < 170000
-// <source_location> not available in libc++ before LLVM 16
-TEST_CASE("custom_error_logger_on_originate", "[!shouldfail]")
-#else
 TEST_CASE("custom_error_logger_on_originate")
-#endif
 {
     // Set up global handler
     REQUIRE(!s_loggerCalled);
diff --git a/test/test_cpp20/format.cpp b/test/test_cpp20/format.cpp
index d16193328..f7c59da39 100644
--- a/test/test_cpp20/format.cpp
+++ b/test/test_cpp20/format.cpp
@@ -1,7 +1,9 @@
-#include "pch.h"
+#include "catch.hpp"
 
-#ifdef __cpp_lib_format
-#include <format>
+import std;
+import winrt.base;
+import Windows.Foundation;
+import Windows.Data.Json;
 
 struct stringable : winrt::implements<stringable, winrt::Windows::Foundation::IStringable>
 {
@@ -37,7 +39,6 @@ TEST_CASE("format_json")
 
 TEST_CASE("format_wstring")
 {
-#if __cpp_lib_format >= 202207L
     {
         std::wstring str = L"World";
         REQUIRE(winrt::format(L"Hello {}", str) == L"Hello World");
@@ -46,6 +47,4 @@ TEST_CASE("format_wstring")
     {
         REQUIRE(winrt::format(L"C++/WinRT #{:d}", 1) == L"C++/WinRT #1");
     }
-#endif
 }
-#endif
diff --git a/test/test_cpp20/hstring.cpp b/test/test_cpp20/hstring.cpp
index 57d145fbb..f81ae641a 100644
--- a/test/test_cpp20/hstring.cpp
+++ b/test/test_cpp20/hstring.cpp
@@ -1,4 +1,7 @@
-#include "pch.h"
+#include "catch.hpp"
+
+import std;
+import winrt.base;
 
 TEST_CASE("hstring")
 {
diff --git a/test/test_cpp20/main.cpp b/test/test_cpp20/main.cpp
index 30687e00c..a6ff65c63 100644
--- a/test/test_cpp20/main.cpp
+++ b/test/test_cpp20/main.cpp
@@ -5,7 +5,8 @@
 #define CATCH_CONFIG_WINDOWS_SEH
 
 #include "catch.hpp"
-#include "winrt/base.h"
+import std;
+import winrt.base;
 
 using namespace winrt;
 
diff --git a/test/test_cpp20/pch.cpp b/test/test_cpp20/pch.cpp
deleted file mode 100644
index 1d9f38c57..000000000
--- a/test/test_cpp20/pch.cpp
+++ /dev/null
@@ -1 +0,0 @@
-#include "pch.h"
diff --git a/test/test_cpp20/pch.h b/test/test_cpp20/pch.h
deleted file mode 100644
index c1a8f5ff3..000000000
--- a/test/test_cpp20/pch.h
+++ /dev/null
@@ -1,17 +0,0 @@
-#pragma once
-
-#pragma warning(4: 4458) // ensure we compile clean with this warning enabled
-
-#define WINRT_LEAN_AND_MEAN
-#include <unknwn.h>
-#include "winrt/Windows.Data.Json.h"
-#include "winrt/Windows.Foundation.h"
-#include "winrt/Windows.Foundation.Collections.h"
-#include "winrt/Windows.Foundation.Numerics.h"
-#include "winrt/Windows.Storage.Streams.h"
-#include <winstring.h>
-#include "catch.hpp"
-
-#include <string_view>
-
-using namespace std::literals;
diff --git a/test/test_cpp20/ranges.cpp b/test/test_cpp20/ranges.cpp
index 9df542696..8ef0b2ba5 100644
--- a/test/test_cpp20/ranges.cpp
+++ b/test/test_cpp20/ranges.cpp
@@ -1,8 +1,7 @@
-#include "pch.h"
+#include "catch.hpp"
 
-#ifdef __cpp_lib_ranges
-#include <algorithm>
-#include <ranges>
+import std;
+import Windows.Foundation.Collections;
 
 TEST_CASE("ranges")
 {
@@ -48,4 +47,3 @@ TEST_CASE("ranges")
         REQUIRE((result == std::vector{ 2, 4, 6 }));
     }
 }
-#endif
diff --git a/test/test_cpp20/test_cpp20.vcxproj b/test/test_cpp20/test_cpp20.vcxproj
index f8eacff83..82cd7eb5c 100644
--- a/test/test_cpp20/test_cpp20.vcxproj
+++ b/test/test_cpp20/test_cpp20.vcxproj
@@ -32,6 +32,7 @@
     <RootNamespace>unittests</RootNamespace>
     <ProjectName>test_cpp20</ProjectName>
     <CppWinRTLanguageStandard>20</CppWinRTLanguageStandard>
+    <BuildStlModules>true</BuildStlModules>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
@@ -99,6 +100,7 @@
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
       <AdditionalOptions Condition="'$(Clang)'=='1'">%(AdditionalOptions) -O3 -flto -fwhole-program-vtables</AdditionalOptions>
@@ -122,6 +124,7 @@
       <Optimization>Disabled</Optimization>
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
@@ -144,6 +147,7 @@
       <Optimization>Disabled</Optimization>
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
@@ -166,6 +170,7 @@
       <Optimization>Disabled</Optimization>
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
@@ -190,6 +195,7 @@
       <IntrinsicFunctions>true</IntrinsicFunctions>
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
@@ -216,6 +222,7 @@
       <IntrinsicFunctions>true</IntrinsicFunctions>
       <AdditionalIncludeDirectories>$(OutputPath);Generated Files;..\</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>NOMINMAX;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
       <WarningLevel>Level4</WarningLevel>
       <TreatWarningAsError>true</TreatWarningAsError>
@@ -236,21 +243,15 @@
     </PostBuildEvent>
   </ItemDefinitionGroup>
   <ItemGroup>
-    <ClInclude Include="pch.h" />
-  </ItemGroup>
-  <ItemGroup>
+    <ClCompile Include="$(CppWinRTDir)winrt\*.ixx" />
+    <ClCompile Include="async.cpp" />
     <ClCompile Include="array_span.cpp" />
     <ClCompile Include="await_completed.cpp" />
     <ClCompile Include="clang_only.cpp" />
     <ClCompile Include="custom_error.cpp" />
     <ClCompile Include="format.cpp" />
     <ClCompile Include="hstring.cpp" />
-    <ClCompile Include="main.cpp">
-      <PrecompiledHeader>NotUsing</PrecompiledHeader>
-    </ClCompile>
-    <ClCompile Include="pch.cpp">
-      <PrecompiledHeader>Create</PrecompiledHeader>
-    </ClCompile>
+    <ClCompile Include="main.cpp" />
     <ClCompile Include="ranges.cpp" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />