diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index b5e60781e0006..184fed2268e81 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -193,17 +193,24 @@ jobs:
             **/crash_diagnostics/*
 
   macos:
-    runs-on: macos-14
     needs: [ stage1 ]
     strategy:
-      fail-fast: true
+      fail-fast: false
       matrix:
-        config: [
-          generic-cxx03,
-          generic-cxx23,
-          generic-modules,
-          apple-configuration
-        ]
+        include:
+        - config: generic-cxx03
+          os: macos-latest
+        - config: generic-cxx23
+          os: macos-latest
+        - config: generic-modules
+          os: macos-latest
+        - config: apple-configuration
+          os: macos-latest
+        - config: apple-system
+          os: macos-13
+        - config: apple-system-hardened
+          os: macos-13
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
       - uses: maxim-lobanov/setup-xcode@v1
diff --git a/libcxx/test/configs/apple-libc++-backdeployment.cfg.in b/libcxx/test/configs/apple-libc++-backdeployment.cfg.in
deleted file mode 100644
index 9843c4a9ad70d..0000000000000
--- a/libcxx/test/configs/apple-libc++-backdeployment.cfg.in
+++ /dev/null
@@ -1,65 +0,0 @@
-# Testing configuration for back-deployment against older Apple system libc++.
-#
-# Under this configuration, we compile and link all the test suite against the latest libc++,
-# however we run against the libc++ on a different platform. This emulates the workflow of
-# a developer building their application using recent tools but with the goal of deploying
-# on existing devices running an older OS (and hence an older dylib).
-
-import os, site
-site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
-import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
-
-lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
-
-BACKDEPLOYMENT_PARAMETERS = [
-    libcxx.test.dsl.Parameter(name='cxx_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{cxx-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++) when running tests.
-
-        This should be a directory hierarchy under which the libc++ dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='abi_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{abi-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++abi) when running tests.
-
-        This should be a directory hierarchy under which the libc++abi dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='unwind_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{unwind-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libunwind) when running tests.
-
-        This should be a directory hierarchy under which the libunwind dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-]
-
-config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
-))
-config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include-dir} -I %{libcxx-dir}/test/support'
-))
-config.substitutions.append(('%{link_flags}',
-    '-nostdlib++ -L %{lib-dir} -lc++'
-))
-config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env DYLD_LIBRARY_PATH="%{cxx-runtime-root}:%{abi-runtime-root}:%{unwind-runtime-root}" -- '
-))
-
-config.stdlib = 'apple-libc++'
-config.using_system_stdlib = True
-
-libcxx.test.config.configure(
-    libcxx.test.params.DEFAULT_PARAMETERS + BACKDEPLOYMENT_PARAMETERS,
-    libcxx.test.features.DEFAULT_FEATURES,
-    config,
-    lit_config
-)
diff --git a/libcxx/test/configs/apple-libc++-system.cfg.in b/libcxx/test/configs/apple-libc++-system.cfg.in
new file mode 100644
index 0000000000000..b59506f375c4a
--- /dev/null
+++ b/libcxx/test/configs/apple-libc++-system.cfg.in
@@ -0,0 +1,33 @@
+# Testing configuration for back-deployment against the system-provided libc++.
+#
+# Under this configuration, we compile and link all the test suite against the just-built
+# libc++, but we run against the system libc++.
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}',
+    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include-dir} -I %{libcxx-dir}/test/support'
+))
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib-dir} -lc++'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T -- '
+))
+
+config.stdlib = 'apple-libc++'
+config.using_system_stdlib = True
+
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/filebuf.members/open_pointer.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.members/open_pointer.pass.cpp
index f070762b3b94d..9f617dc1e5a89 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/filebuf.members/open_pointer.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.members/open_pointer.pass.cpp
@@ -10,6 +10,9 @@
 
 // basic_filebuf<charT,traits>* open(const char* s, ios_base::openmode mode);
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <fstream>
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/setbuf.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/setbuf.pass.cpp
index 8bcce28162033..10435dc482367 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/setbuf.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/filebuf.virtuals/setbuf.pass.cpp
@@ -10,6 +10,9 @@
 
 // basic_streambuf<charT, traits>* setbuf(char_type* s, streamsize n) override;
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 #include <fstream>
 #include <cstddef>
 #include <cassert>
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/fstream.cons/pointer.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/fstream.cons/pointer.pass.cpp
index df7d3b948e327..2e0ebcd684d79 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/fstream.cons/pointer.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/fstream.cons/pointer.pass.cpp
@@ -13,6 +13,9 @@
 
 // explicit basic_fstream(const char* s, ios_base::openmode mode = ios_base::in | ios_base::out);
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <fstream>
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/fstream.members/open_pointer.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/fstream.members/open_pointer.pass.cpp
index 790b9ef02f902..0d83d681b1dfc 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/fstream.members/open_pointer.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/fstream.members/open_pointer.pass.cpp
@@ -13,6 +13,9 @@
 
 // void open(const char* s, ios_base::openmode mode = ios_base::in|ios_base::out);
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <fstream>
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp
index af43ffdbf8006..fbb03f1e85841 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/ofstream.cons/pointer.pass.cpp
@@ -13,6 +13,9 @@
 
 // explicit basic_ofstream(const char* s, ios_base::openmode mode = ios_base::out);
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <fstream>
diff --git a/libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/open_pointer.pass.cpp b/libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/open_pointer.pass.cpp
index b0a68fd4340b7..73a474277a933 100644
--- a/libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/open_pointer.pass.cpp
+++ b/libcxx/test/std/input.output/file.streams/fstreams/ofstream.members/open_pointer.pass.cpp
@@ -13,6 +13,9 @@
 
 // void open(const char* s, ios_base::openmode mode = ios_base::out);
 
+// In C++23 and later, this test requires support for P2467R1 in the dylib (a3f17ba3febbd546f2342ffc780ac93b694fdc8d)
+// XFAIL: (!c++03 && !c++11 && !c++14 && !c++17 && !c++20) && using-built-library-before-llvm-18
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <fstream>
diff --git a/libcxx/test/std/input.output/string.streams/stringstream/stringstream.members/gcount.pass.cpp b/libcxx/test/std/input.output/string.streams/stringstream/stringstream.members/gcount.pass.cpp
index a9079dc63b6b5..84004dc12f11a 100644
--- a/libcxx/test/std/input.output/string.streams/stringstream/stringstream.members/gcount.pass.cpp
+++ b/libcxx/test/std/input.output/string.streams/stringstream/stringstream.members/gcount.pass.cpp
@@ -9,6 +9,9 @@
 // UNSUPPORTED: 32-bit-pointer
 // REQUIRES: large_tests
 
+// This bug was fixed in the dylib by 53aed4759b33e33614e0f4e321bc1ef764b6d5b6.
+// XFAIL: using-built-library-before-llvm-17
+
 // Android devices frequently don't have enough memory to run this test. Rather
 // than throw std::bad_alloc, exhausting memory triggers the OOM Killer.
 // UNSUPPORTED: LIBCXX-ANDROID-FIXME
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
index 906df734bc42b..d1465721cf164 100644
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -37,48 +37,6 @@ definitions:
       - "**/crash_diagnostics/*"
 
 steps:
-- group: ':mac: Apple'
-  steps:
-  - label: Apple back-deployment macosx10.13
-    command: libcxx/utils/ci/run-buildbot apple-system-backdeployment-10.13
-    agents:
-      queue: libcxx-builders
-      os: macos
-      arch: x86_64 # We need to use x86_64 for back-deployment CI on this target since macOS didn't support arm64 back then
-    <<: *common
-
-  - label: Apple back-deployment macosx10.15
-    command: libcxx/utils/ci/run-buildbot apple-system-backdeployment-10.15
-    agents:
-      queue: libcxx-builders
-      os: macos
-      arch: x86_64 # We need to use x86_64 for back-deployment CI on this target since macOS didn't support arm64 back then
-    <<: *common
-
-  - label: Apple back-deployment with hardening enabled
-    command: libcxx/utils/ci/run-buildbot apple-system-backdeployment-hardened-11.0
-    agents:
-      queue: libcxx-builders
-      os: macos
-      arch: x86_64 # TODO: Remove this once we are able to run back-deployment on arm64 again, since this isn't x86_64 specific
-    <<: *common
-
-    # TODO: Re-enable this once we've figured out how to run back-deployment testing on arm64 on recent OSes
-    # - label: "Apple back-deployment macosx11.0 arm64"
-    #   command: "libcxx/utils/ci/run-buildbot apple-system-backdeployment-11.0"
-    #   artifact_paths:
-    #     - "**/test-results.xml"
-    #     - "**/*.abilist"
-    #   agents:
-    #     queue: "libcxx-builders"
-    #     os: "macos"
-    #     arch: "arm64"
-    #   retry:
-    #     automatic:
-    #       - exit_status: -1  # Agent was lost
-    #         limit: 2
-    #   timeout_in_minutes: 120
-
 - group: ARM
   steps:
   - label: AArch64
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
index b0533cb9a49c9..a82d121838703 100755
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -522,80 +522,94 @@ apple-configuration)
     # TODO: It would be better to run the tests against the fake-installed version of libc++ instead
     xcrun --sdk macosx ninja -vC "${BUILD_DIR}/${arch}" check-cxx check-cxxabi check-cxx-abilist
 ;;
-apple-system-backdeployment-hardened-*)
+apple-system-hardened)
     clean
 
-    if [[ "${OSX_ROOTS}" == "" ]]; then
-        echo "--- Downloading previous macOS dylibs"
-        PREVIOUS_DYLIBS_URL="https://dl.dropboxusercontent.com/s/gmcfxwgl9f9n6pu/libcxx-roots.tar.gz"
-        OSX_ROOTS="${BUILD_DIR}/macos-roots"
-        mkdir -p "${OSX_ROOTS}"
-        curl "${PREVIOUS_DYLIBS_URL}" | tar -xz --strip-components=1 -C "${OSX_ROOTS}"
-    fi
+    arch="$(uname -m)"
+    version="$(sw_vers --productVersion)"
+    params="target_triple=${arch}-apple-macosx${version}"
+    params+=";hardening_mode=fast"
 
-    DEPLOYMENT_TARGET="${BUILDER#apple-system-backdeployment-hardened-}"
+    # In the Apple system configuration, we build libc++ and libunwind separately.
+    ${CMAKE} \
+        -S "${MONOREPO_ROOT}/runtimes" \
+        -B "${BUILD_DIR}/cxx" \
+        -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
+        -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+        -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}/cxx" \
+        -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
+        -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+        -DLIBCXX_CXX_ABI=libcxxabi \
+        -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Apple.cmake" \
+        -DLIBCXX_TEST_CONFIG="apple-libc++-system.cfg.in" \
+        -DLIBCXXABI_TEST_CONFIG="apple-libc++abi-system.cfg.in" \
+        -DLIBCXX_TEST_PARAMS="${params}" \
+        -DLIBCXXABI_TEST_PARAMS="${params}"
 
-    # TODO: On Apple platforms, we never produce libc++abi.1.dylib or libunwind.1.dylib,
-    #       only libc++abi.dylib and libunwind.dylib. Fix that in the build so that the
-    #       tests stop searching for @rpath/libc++abi.1.dylib and @rpath/libunwind.1.dylib.
-    cp "${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}/libc++abi.dylib" \
-       "${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}/libc++abi.1.dylib"
-    cp "${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}/libunwind.dylib" \
-       "${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}/libunwind.1.dylib"
+    ${CMAKE} \
+        -S "${MONOREPO_ROOT}/runtimes" \
+        -B "${BUILD_DIR}/unwind" \
+        -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
+        -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+        -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}/unwind" \
+        -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
+        -DLLVM_ENABLE_RUNTIMES="libunwind" \
+        -DLIBUNWIND_TEST_CONFIG="apple-libunwind-system.cfg.in" \
+        -DLIBUNWIND_TEST_PARAMS="${params}" \
+        -DCMAKE_INSTALL_NAME_DIR="/usr/lib/system"
 
-    arch="$(uname -m)"
-    PARAMS="target_triple=${arch}-apple-macosx${DEPLOYMENT_TARGET}"
-    PARAMS+=";cxx_runtime_root=${OSX_ROOTS}/macOS/libc++/${DEPLOYMENT_TARGET}"
-    PARAMS+=";abi_runtime_root=${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}"
-    PARAMS+=";unwind_runtime_root=${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}"
-    PARAMS+=";hardening_mode=fast"
+    echo "+++ Running the libc++ tests"
+    ${NINJA} -vC "${BUILD_DIR}/cxx" check-cxx
 
-    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Apple.cmake" \
-                   -DLIBCXX_TEST_CONFIG="apple-libc++-backdeployment.cfg.in" \
-                   -DLIBCXXABI_TEST_CONFIG="apple-libc++abi-backdeployment.cfg.in" \
-                   -DLIBUNWIND_TEST_CONFIG="apple-libunwind-backdeployment.cfg.in" \
-                   -DLIBCXX_TEST_PARAMS="${PARAMS}" \
-                   -DLIBCXXABI_TEST_PARAMS="${PARAMS}" \
-                   -DLIBUNWIND_TEST_PARAMS="${PARAMS}"
+    echo "+++ Running the libc++abi tests"
+    ${NINJA} -vC "${BUILD_DIR}/cxx" check-cxxabi
 
-    check-runtimes
+    echo "+++ Running the libunwind tests"
+    ${NINJA} -vC "${BUILD_DIR}/unwind" check-unwind
 ;;
-apple-system-backdeployment-*)
+apple-system)
     clean
 
-    if [[ "${OSX_ROOTS}" == "" ]]; then
-        echo "--- Downloading previous macOS dylibs"
-        PREVIOUS_DYLIBS_URL="https://dl.dropboxusercontent.com/s/gmcfxwgl9f9n6pu/libcxx-roots.tar.gz"
-        OSX_ROOTS="${BUILD_DIR}/macos-roots"
-        mkdir -p "${OSX_ROOTS}"
-        curl "${PREVIOUS_DYLIBS_URL}" | tar -xz --strip-components=1 -C "${OSX_ROOTS}"
-    fi
+    arch="$(uname -m)"
+    version="$(sw_vers --productVersion)"
+    params="target_triple=${arch}-apple-macosx${version}"
 
-    DEPLOYMENT_TARGET="${BUILDER#apple-system-backdeployment-}"
+    # In the Apple system configuration, we build libc++ and libunwind separately.
+    ${CMAKE} \
+        -S "${MONOREPO_ROOT}/runtimes" \
+        -B "${BUILD_DIR}/cxx" \
+        -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
+        -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+        -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}/cxx" \
+        -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
+        -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+        -DLIBCXX_CXX_ABI=libcxxabi \
+        -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Apple.cmake" \
+        -DLIBCXX_TEST_CONFIG="apple-libc++-system.cfg.in" \
+        -DLIBCXXABI_TEST_CONFIG="apple-libc++abi-system.cfg.in" \
+        -DLIBCXX_TEST_PARAMS="${params}" \
+        -DLIBCXXABI_TEST_PARAMS="${params}"
 
-    # TODO: On Apple platforms, we never produce libc++abi.1.dylib or libunwind.1.dylib,
-    #       only libc++abi.dylib and libunwind.dylib. Fix that in the build so that the
-    #       tests stop searching for @rpath/libc++abi.1.dylib and @rpath/libunwind.1.dylib.
-    cp "${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}/libc++abi.dylib" \
-       "${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}/libc++abi.1.dylib"
-    cp "${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}/libunwind.dylib" \
-       "${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}/libunwind.1.dylib"
+    ${CMAKE} \
+        -S "${MONOREPO_ROOT}/runtimes" \
+        -B "${BUILD_DIR}/unwind" \
+        -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
+        -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+        -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}/unwind" \
+        -DLLVM_LIT_ARGS="-sv --xunit-xml-output test-results.xml --timeout=1500 --time-tests" \
+        -DLLVM_ENABLE_RUNTIMES="libunwind" \
+        -DLIBUNWIND_TEST_CONFIG="apple-libunwind-system.cfg.in" \
+        -DLIBUNWIND_TEST_PARAMS="${params}" \
+        -DCMAKE_INSTALL_NAME_DIR="/usr/lib/system"
 
-    arch="$(uname -m)"
-    PARAMS="target_triple=${arch}-apple-macosx${DEPLOYMENT_TARGET}"
-    PARAMS+=";cxx_runtime_root=${OSX_ROOTS}/macOS/libc++/${DEPLOYMENT_TARGET}"
-    PARAMS+=";abi_runtime_root=${OSX_ROOTS}/macOS/libc++abi/${DEPLOYMENT_TARGET}"
-    PARAMS+=";unwind_runtime_root=${OSX_ROOTS}/macOS/libunwind/${DEPLOYMENT_TARGET}"
+    echo "+++ Running the libc++ tests"
+    ${NINJA} -vC "${BUILD_DIR}/cxx" check-cxx
 
-    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Apple.cmake" \
-                   -DLIBCXX_TEST_CONFIG="apple-libc++-backdeployment.cfg.in" \
-                   -DLIBCXXABI_TEST_CONFIG="apple-libc++abi-backdeployment.cfg.in" \
-                   -DLIBUNWIND_TEST_CONFIG="apple-libunwind-backdeployment.cfg.in" \
-                   -DLIBCXX_TEST_PARAMS="${PARAMS}" \
-                   -DLIBCXXABI_TEST_PARAMS="${PARAMS}" \
-                   -DLIBUNWIND_TEST_PARAMS="${PARAMS}"
+    echo "+++ Running the libc++abi tests"
+    ${NINJA} -vC "${BUILD_DIR}/cxx" check-cxxabi
 
-    check-runtimes
+    echo "+++ Running the libunwind tests"
+    ${NINJA} -vC "${BUILD_DIR}/unwind" check-unwind
 ;;
 benchmarks)
     clean
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
index 29810c8ffee53..735eb5ac949dc 100644
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -620,21 +620,21 @@ def check_gdb(cfg):
     Feature(
         name="_target-has-llvm-17",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-18 || target={{.+}}-apple-macosx{{14.[4-9](.0)?}} || target={{.+}}-apple-macosx{{1[5-9]([.].+)?}}",
+            "_target-has-llvm-18 || target={{.+}}-apple-macosx{{14.[4-9](.[0-9]+)?}} || target={{.+}}-apple-macosx{{1[5-9]([.].+)?}}",
             cfg.available_features,
         ),
     ),
     Feature(
         name="_target-has-llvm-16",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-17 || target={{.+}}-apple-macosx{{14.[0-3](.0)?}}",
+            "_target-has-llvm-17 || target={{.+}}-apple-macosx{{14.[0-3](.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
     Feature(
         name="_target-has-llvm-15",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-16 || target={{.+}}-apple-macosx{{13.[4-9](.0)?}}",
+            "_target-has-llvm-16 || target={{.+}}-apple-macosx{{13.[4-9](.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
@@ -648,21 +648,21 @@ def check_gdb(cfg):
     Feature(
         name="_target-has-llvm-13",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-14 || target={{.+}}-apple-macosx{{13.[0-3](.0)?}}",
+            "_target-has-llvm-14 || target={{.+}}-apple-macosx{{13.[0-3](.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
     Feature(
         name="_target-has-llvm-12",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-13 || target={{.+}}-apple-macosx{{12.[3-9](.0)?}}",
+            "_target-has-llvm-13 || target={{.+}}-apple-macosx{{12.[3-9](.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
     Feature(
         name="_target-has-llvm-11",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-12 || target={{.+}}-apple-macosx{{(11.[0-9]|12.[0-2])(.0)?}}",
+            "_target-has-llvm-12 || target={{.+}}-apple-macosx{{(11.[0-9]|12.[0-2])(.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
@@ -676,7 +676,7 @@ def check_gdb(cfg):
     Feature(
         name="_target-has-llvm-9",
         when=lambda cfg: BooleanExpression.evaluate(
-            "_target-has-llvm-10 || target={{.+}}-apple-macosx{{10.15(.0)?}}",
+            "_target-has-llvm-10 || target={{.+}}-apple-macosx{{10.15(.[0-9]+)?}}",
             cfg.available_features,
         ),
     ),
@@ -719,7 +719,7 @@ def check_gdb(cfg):
 # a libc++ flavor that enables availability markup. Similarly, a test could fail when
 # run against the system library of an older version of FreeBSD, even though FreeBSD
 # doesn't provide availability markup at the time of writing this.
-for version in ("9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19"):
+for version in ("9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20"):
     DEFAULT_FEATURES.append(
         Feature(
             name="using-built-library-before-llvm-{}".format(version),
@@ -755,27 +755,27 @@ def check_gdb(cfg):
             cfg.available_features,
         ),
     ),
-    # Tests that require __libcpp_verbose_abort support in the built library
+    # Tests that require std::to_chars(floating-point) in the built library
     Feature(
-        name="availability-verbose_abort-missing",
+        name="availability-fp_to_chars-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-13)",
+            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-14)",
             cfg.available_features,
         ),
     ),
-    # Tests that require std::pmr support in the built library
+    # Tests that require __libcpp_verbose_abort support in the built library
     Feature(
-        name="availability-pmr-missing",
+        name="availability-verbose_abort-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-13)",
+            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-15)",
             cfg.available_features,
         ),
     ),
-    # Tests that require std::to_chars(floating-point) in the built library
+    # Tests that require std::pmr support in the built library
     Feature(
-        name="availability-fp_to_chars-missing",
+        name="availability-pmr-missing",
         when=lambda cfg: BooleanExpression.evaluate(
-            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-14)",
+            "!libcpp-has-no-availability-markup && (stdlib=apple-libc++ && !_target-has-llvm-16)",
             cfg.available_features,
         ),
     ),
diff --git a/libcxxabi/test/configs/apple-libc++abi-backdeployment.cfg.in b/libcxxabi/test/configs/apple-libc++abi-backdeployment.cfg.in
deleted file mode 100644
index 9e725c523f29b..0000000000000
--- a/libcxxabi/test/configs/apple-libc++abi-backdeployment.cfg.in
+++ /dev/null
@@ -1,66 +0,0 @@
-# Testing configuration for back-deployment against older Apple system libc++abi.
-#
-# Under this configuration, we compile and link all the test suite against the latest libc++abi,
-# however we run against the libc++abi on a different platform. This emulates the workflow of
-# a developer building their application using recent tools but with the goal of deploying
-# on existing devices running an older OS (and hence an older dylib).
-
-import os, site
-site.addsitedir(os.path.join('@LIBCXXABI_LIBCXX_PATH@', 'utils'))
-import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
-
-lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
-
-BACKDEPLOYMENT_PARAMETERS = [
-    libcxx.test.dsl.Parameter(name='cxx_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{cxx-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++) when running tests.
-
-        This should be a directory hierarchy under which the libc++ dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='abi_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{abi-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++abi) when running tests.
-
-        This should be a directory hierarchy under which the libc++abi dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='unwind_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{unwind-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libunwind) when running tests.
-
-        This should be a directory hierarchy under which the libunwind dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-]
-
-config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
-))
-config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
-    '-I %{libcxx}/test/support -I %{libcxx}/src'
-))
-config.substitutions.append(('%{link_flags}',
-    '-nostdlib++ -L %{lib} -lc++ -lc++abi'
-))
-config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env DYLD_LIBRARY_PATH="%{cxx-runtime-root}:%{abi-runtime-root}:%{unwind-runtime-root}" -- '
-))
-
-config.stdlib = 'apple-libc++'
-config.using_system_stdlib = True
-
-libcxx.test.config.configure(
-    libcxx.test.params.DEFAULT_PARAMETERS + BACKDEPLOYMENT_PARAMETERS,
-    libcxx.test.features.DEFAULT_FEATURES,
-    config,
-    lit_config
-)
diff --git a/libcxxabi/test/configs/apple-libc++abi-system.cfg.in b/libcxxabi/test/configs/apple-libc++abi-system.cfg.in
new file mode 100644
index 0000000000000..1e80eee4f8d0c
--- /dev/null
+++ b/libcxxabi/test/configs/apple-libc++abi-system.cfg.in
@@ -0,0 +1,34 @@
+# Testing configuration for back-deployment against the system-provided libc++abi.
+#
+# Under this configuration, we compile and link all the test suite against the just-built
+# libc++abi, but we run against the system libc++abi.
+
+import os, site
+site.addsitedir(os.path.join('@LIBCXXABI_LIBCXX_PATH@', 'utils'))
+import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}',
+    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
+    '-I %{libcxx}/test/support -I %{libcxx}/src'
+))
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib} -lc++'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T -- '
+))
+
+config.stdlib = 'apple-libc++'
+config.using_system_stdlib = True
+
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)
diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp
index eb32b4679aff0..ad131bb3a8a7b 100644
--- a/libcxxabi/test/test_demangle.pass.cpp
+++ b/libcxxabi/test/test_demangle.pass.cpp
@@ -9,9 +9,8 @@
 // This test is too big for most embedded devices.
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 
-// https://llvm.org/PR51407 was not fixed in some previously-released
-// demanglers, which causes them to run into the infinite loop.
-// UNSUPPORTED: using-built-library-before-llvm-14
+// This test exercises support for char array initializer lists added in dd8b266ef.
+// UNSUPPORTED: using-built-library-before-llvm-20
 
 // Android's long double on x86[-64] is (64/128)-bits instead of Linux's usual
 // 80-bit format, and this demangling test is failing on it.
diff --git a/libunwind/test/configs/apple-libunwind-backdeployment.cfg.in b/libunwind/test/configs/apple-libunwind-backdeployment.cfg.in
deleted file mode 100644
index 013c43ae78001..0000000000000
--- a/libunwind/test/configs/apple-libunwind-backdeployment.cfg.in
+++ /dev/null
@@ -1,67 +0,0 @@
-# Testing configuration for back-deployment against older Apple system libunwind.
-#
-# Under this configuration, we compile and link all the test suite against the latest libunwind,
-# however we run against the libunwind on a different platform. This emulates the workflow of
-# a developer building their application using recent tools but with the goal of deploying
-# on existing devices running an older OS (and hence an older dylib).
-
-import os, site
-site.addsitedir(os.path.join('@LIBUNWIND_LIBCXX_PATH@', 'utils'))
-import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
-
-lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
-
-BACKDEPLOYMENT_PARAMETERS = [
-    libcxx.test.dsl.Parameter(name='cxx_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{cxx-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++) when running tests.
-
-        This should be a directory hierarchy under which the libc++ dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='abi_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{abi-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libc++abi) when running tests.
-
-        This should be a directory hierarchy under which the libc++abi dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-    libcxx.test.dsl.Parameter(name='unwind_runtime_root', type=str,
-        actions=lambda root: [libcxx.test.dsl.AddSubstitution('%{unwind-runtime-root}', root)],
-        help="""
-        The simulated root of the system (for libunwind) when running tests.
-
-        This should be a directory hierarchy under which the libunwind dylib can be found.
-        The dylib in that hierarchy is the one that will be used at runtime when running
-        the tests.
-        """),
-]
-
-config.substitutions.append(('%{flags}',
-    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
-))
-config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -I %{include}'
-))
-config.substitutions.append(('%{link_flags}',
-    '-nostdlib++ -L %{lib} -lc++ -lc++abi -lunwind'
-))
-config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env DYLD_LIBRARY_PATH="%{cxx-runtime-root}:%{abi-runtime-root}:%{unwind-runtime-root}" -- '
-))
-
-config.stdlib = 'apple-libc++'
-config.using_system_stdlib = True
-
-import os, site
-import libcxx.test.params, libcxx.test.config
-libcxx.test.config.configure(
-    libcxx.test.params.DEFAULT_PARAMETERS + BACKDEPLOYMENT_PARAMETERS,
-    libcxx.test.features.DEFAULT_FEATURES,
-    config,
-    lit_config
-)
diff --git a/libunwind/test/configs/apple-libunwind-system.cfg.in b/libunwind/test/configs/apple-libunwind-system.cfg.in
new file mode 100644
index 0000000000000..e5a7c983562a6
--- /dev/null
+++ b/libunwind/test/configs/apple-libunwind-system.cfg.in
@@ -0,0 +1,41 @@
+# Testing configuration for back-deployment against the system-provided libunwind.
+#
+# Under this configuration, we compile and link all the test suite against the just-built
+# libunwind, but we run against the system libunwind.
+
+import os, site
+site.addsitedir(os.path.join('@LIBUNWIND_LIBCXX_PATH@', 'utils'))
+import libcxx.test.params, libcxx.test.config, libcxx.test.dsl
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+config.substitutions.append(('%{flags}',
+    '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include}'
+))
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib} -lc++ -lunwind'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor} --execdir %T -- '
+))
+
+config.stdlib = 'apple-libc++'
+config.using_system_stdlib = True
+
+# TODO: This is a giant hack, but we need to change the install_name of libunwind.dylib because the
+#       upstream configuration can't currently produce a libunwind.dylib that is compatible with the
+#       Apple system one.
+import subprocess
+subprocess.check_call(['install_name_tool', '-id', '/usr/lib/system/libunwind.dylib', '@LIBUNWIND_TESTING_INSTALL_PREFIX@/lib/libunwind.dylib'])
+
+import os, site
+import libcxx.test.params, libcxx.test.config
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)