diff --git a/CMakeLists.txt b/CMakeLists.txt
index f04d3d39c98..d6289e713e6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,8 +6,8 @@ cmake_minimum_required(VERSION 4.1.1)
 set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
 project(msvc_standard_libraries LANGUAGES CXX)
 
-if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.50.35717")
-    message(FATAL_ERROR "The STL must be built with MSVC Compiler 19.50.35717 or later.")
+if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.50.35719")
+    message(FATAL_ERROR "The STL must be built with MSVC Compiler 19.50.35719 or later.")
 endif()
 
 include(CheckCXXSourceCompiles)
@@ -46,7 +46,7 @@ if(TARGET run-validate)
     add_dependencies(validate run-validate)
 endif()
 
-option(BUILD_TESTING "Enable testing" ON)
+option(CONFIGURE_TESTING "Enable testing" ON)
 set(VCLIBS_SUFFIX "_oss" CACHE STRING "suffix for built DLL names to avoid conflicts with distributed DLLs")
 
 option(STL_USE_ANALYZE "Pass the /analyze flag to MSVC" OFF)
@@ -115,7 +115,7 @@ set(VCLIBS_DEBUG_OPTIONS "$<$<COMPILE_LANGUAGE:CXX>:/Od>")
 # TRANSITION, GH-2108: Investigate building the STL with only /O2, not /Os.
 set(VCLIBS_RELEASE_OPTIONS "$<$<COMPILE_LANGUAGE:CXX>:/O2;/Os>")
 
-if(BUILD_TESTING)
+if(CONFIGURE_TESTING)
     add_subdirectory(tests)
 endif()
 
diff --git a/azure-devops/build-and-test.yml b/azure-devops/build-and-test.yml
index 11cf23afa94..250856fb8e1 100644
--- a/azure-devops/build-and-test.yml
+++ b/azure-devops/build-and-test.yml
@@ -23,9 +23,15 @@ parameters:
 - name: numShards
   type: number
   default: 8
-- name: skipTesting
+- name: configureTesting
   type: boolean
-  default: false
+  default: true
+- name: buildStl
+  type: boolean
+  default: true
+- name: runTesting
+  type: boolean
+  default: true
 - name: testsBuildOnly
   type: boolean
   default: false
@@ -38,7 +44,7 @@ jobs:
   - template: checkout-self.yml
   - template: checkout-submodule.yml
     parameters:
-      enabled: ${{ not(parameters.skipTesting) }}
+      enabled: ${{ parameters.configureTesting }}
       path: 'llvm-project'
       url: 'https://github.com/llvm/llvm-project.git'
   - template: checkout-submodule.yml
@@ -58,6 +64,8 @@ jobs:
       targetPlatform: ${{ parameters.targetPlatform }}
       analyzeBuild: ${{ parameters.analyzeBuild }}
       asanBuild: ${{ parameters.asanBuild }}
+      configureTesting: ${{ parameters.configureTesting }}
+      buildStl: ${{ parameters.buildStl }}
       testsBuildOnly: ${{ parameters.testsBuildOnly }}
   - template: build-benchmarks.yml
     parameters:
@@ -79,4 +87,4 @@ jobs:
       targetArch: ${{ parameters.targetArch }}
       targetPlatform: ${{ parameters.targetPlatform }}
       testTargets: ${{ parameters.testTargets }}
-      skipTesting: ${{ parameters.skipTesting }}
+      runTesting: ${{ parameters.runTesting }}
diff --git a/azure-devops/build-benchmarks.yml b/azure-devops/build-benchmarks.yml
index 39bc4a3e325..031e3b2adff 100644
--- a/azure-devops/build-benchmarks.yml
+++ b/azure-devops/build-benchmarks.yml
@@ -25,7 +25,7 @@ steps:
     -DSTL_BINARY_DIR="$(buildOutputLocation)" ^
     -DVCLIBS_TARGET_ARCHITECTURE=${{ parameters.targetPlatform }} ^
     -S $(Build.SourcesDirectory)/benchmarks -B "$(benchmarkBuildOutputLocation)\${{ parameters.compiler }}"
-  displayName: 'Configure the benchmarks for ${{ parameters.compiler }}'
+  displayName: 'Configure Benchmarks for ${{ parameters.compiler }}'
   timeoutInMinutes: 2
   env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
   # TRANSITION, we currently only build the benchmarks with Clang for x64
@@ -36,7 +36,7 @@ steps:
 - script: |
     call "$(vsDevCmdBat)" -host_arch=${{ parameters.hostArch }} -arch=${{ parameters.targetArch }} -no_logo
     cmake --build "$(benchmarkBuildOutputLocation)\${{ parameters.compiler }}"
-  displayName: 'Build the benchmarks for ${{ parameters.compiler }}'
+  displayName: 'Build Benchmarks for ${{ parameters.compiler }}'
   timeoutInMinutes: 2
   env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
   # TRANSITION, we currently only build the benchmarks with Clang for x64
diff --git a/azure-devops/checkout-self.yml b/azure-devops/checkout-self.yml
index 69fbb011639..711c2b00321 100644
--- a/azure-devops/checkout-self.yml
+++ b/azure-devops/checkout-self.yml
@@ -14,4 +14,4 @@ steps:
   retryCountOnTaskFailure: 4
 - script: |
     git clean --quiet -x -d -f -f
-  displayName: 'Clean after checkout'
+  displayName: 'Clean After Checkout'
diff --git a/azure-devops/cmake-configure-build.yml b/azure-devops/cmake-configure-build.yml
index d60b672bd3a..8fa87a301c8 100644
--- a/azure-devops/cmake-configure-build.yml
+++ b/azure-devops/cmake-configure-build.yml
@@ -12,6 +12,10 @@ parameters:
   type: boolean
 - name: asanBuild
   type: boolean
+- name: configureTesting
+  type: boolean
+- name: buildStl
+  type: boolean
 - name: testsBuildOnly
   type: boolean
 - name: litFlags
@@ -34,15 +38,17 @@ steps:
     -DLIT_FLAGS=${{ join(';', parameters.litFlags) }} ^
     -DSTL_USE_ANALYZE=${{ parameters.analyzeBuild }} ^
     -DSTL_ASAN_BUILD=${{ parameters.asanBuild }} ^
+    -DCONFIGURE_TESTING=${{ parameters.configureTesting }} ^
     -DTESTS_BUILD_ONLY=${{ parameters.testsBuildOnly }} ^
     -DVCLIBS_TARGET_ARCHITECTURE=${{ parameters.targetPlatform }} ^
     -S $(Build.SourcesDirectory) -B "$(buildOutputLocation)"
-  displayName: 'Configure the STL'
+  displayName: 'Configure STL'
   timeoutInMinutes: 2
   env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
 - script: |
     call "$(vsDevCmdBat)" -host_arch=${{ parameters.hostArch }} -arch=${{ parameters.targetArch }} -no_logo
     cmake --build "$(buildOutputLocation)"
-  displayName: 'Build the STL'
+  displayName: 'Build STL'
   timeoutInMinutes: 5
+  condition: and(succeeded(), ${{ parameters.buildStl }})
   env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
diff --git a/azure-devops/config.yml b/azure-devops/config.yml
index de675864e2d..2c6fd986603 100644
--- a/azure-devops/config.yml
+++ b/azure-devops/config.yml
@@ -5,10 +5,10 @@
 
 variables:
 - name: poolName
-  value: 'Stl-2025-11-17T2154-x64-Pool'
+  value: 'Stl-2025-11-24T1624-x64-Pool'
   readonly: true
 - name: arm64PoolName
-  value: 'Stl-2025-11-17T2237-arm64-Pool'
+  value: 'Stl-2025-11-24T1624-arm64-Pool'
   readonly: true
 - name: poolDemands
   value: 'EnableSpotVM -equals false'
diff --git a/azure-devops/create-1es-hosted-pool.ps1 b/azure-devops/create-1es-hosted-pool.ps1
index d4ab87f4d04..9a00ad3c3f4 100644
--- a/azure-devops/create-1es-hosted-pool.ps1
+++ b/azure-devops/create-1es-hosted-pool.ps1
@@ -29,8 +29,9 @@ if ($Arch -ieq 'x64') {
   $ImageOffer = 'WindowsServer'
   $ImageSku = '2025-datacenter-azure-edition'
 } else {
-  $AvailableLocations = @('eastus2', 'northeurope') # Locations where CPP_STL_GitHub has obtained sufficient quota.
-  $AvailableLocationIdx = 1 # Increment for each new pool, to cycle through the available locations.
+  # CPP_STL_GitHub has quota for 672 cores (21 VMs) in westcentralus, not currently used.
+  $AvailableLocations = @('eastus2', 'northeurope') # Locations where CPP_STL_GitHub has quota for 1024 cores (32 VMs).
+  $AvailableLocationIdx = 2 # Increment for each new pool, to cycle through the available locations.
   $Location = $AvailableLocations[$AvailableLocationIdx % $AvailableLocations.Length]
   $VMSize = 'Standard_D32ps_v6'
   $PoolSize = 32
diff --git a/azure-devops/format-validation.yml b/azure-devops/format-validation.yml
index b9345716379..77f3635e5b2 100644
--- a/azure-devops/format-validation.yml
+++ b/azure-devops/format-validation.yml
@@ -16,7 +16,7 @@ jobs:
         call "$(vsDevCmdBat)" -host_arch=x64 -arch=x64 -no_logo
         cmake -G Ninja -S $(Build.SourcesDirectory)/tools -B "$(validationBuildOutputLocation)"
         cmake --build "$(validationBuildOutputLocation)"
-      displayName: 'Build format and validation'
+      displayName: 'Build Validation Tools'
       timeoutInMinutes: 5
       env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
     - script: |
diff --git a/azure-devops/run-tests.yml b/azure-devops/run-tests.yml
index 22357e528fe..847adccb36d 100644
--- a/azure-devops/run-tests.yml
+++ b/azure-devops/run-tests.yml
@@ -10,21 +10,21 @@ parameters:
   type: string
 - name: testTargets
   type: string
-- name: skipTesting
+- name: runTesting
   type: boolean
 steps:
 - script: |
     call "$(vsDevCmdBat)" -host_arch=${{ parameters.hostArch }} -arch=${{ parameters.targetArch }} -no_logo
     ninja --verbose -k 0 ${{ parameters.testTargets }}
-  displayName: 'Build and Run Tests'
+  displayName: 'Run Tests'
   timeoutInMinutes: 30
-  condition: and(succeeded(), not(${{ parameters.skipTesting }}))
+  condition: and(succeeded(), ${{ parameters.runTesting }})
   workingDirectory: $(buildOutputLocation)
   env: { TMP: $(tmpDir), TEMP: $(tmpDir) }
 - task: PublishTestResults@2
   displayName: 'Publish Tests'
   timeoutInMinutes: 5
-  condition: and(succeededOrFailed(), not(${{ parameters.skipTesting }}))
+  condition: and(succeededOrFailed(), ${{ parameters.runTesting }})
   inputs:
     searchFolder: $(buildOutputLocation)
     testResultsFormat: JUnit
@@ -32,5 +32,5 @@ steps:
     testRunTitle: 'test-${{ parameters.targetPlatform }}-$(System.JobPositionInPhase)'
 - publish: $(buildOutputLocation)/test-results.xml
   artifact: '${{ parameters.targetPlatform }}-$(System.JobPositionInPhase)-xml-$(System.JobId)'
-  condition: and(failed(), not(${{ parameters.skipTesting }}))
+  condition: and(failed(), ${{ parameters.runTesting }})
   displayName: 'Publish XML Artifact'
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 98f36d52a6b..8776d9901e2 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -34,7 +34,8 @@ stages:
           analyzeBuild: true
           buildBenchmarks: true
           numShards: 1
-          skipTesting: true
+          configureTesting: false
+          runTesting: false
 
   - stage: Build_x86
     dependsOn: []
@@ -51,7 +52,8 @@ stages:
           analyzeBuild: true
           buildBenchmarks: true
           numShards: 1
-          skipTesting: true
+          configureTesting: false
+          runTesting: false
 
   - stage: Build_ARM64_Cross
     dependsOn: []
@@ -68,7 +70,8 @@ stages:
           analyzeBuild: true
           buildBenchmarks: true
           numShards: 1
-          skipTesting: true
+          configureTesting: false
+          runTesting: false
 
   - stage: Build_ARM64EC_Cross
     dependsOn: []
@@ -85,7 +88,8 @@ stages:
           analyzeBuild: true
           buildBenchmarks: true
           numShards: 1
-          skipTesting: true
+          configureTesting: false
+          runTesting: false
 
   # This ARM64-native build will detect problems with the ARM64 pool as early as possible.
   # The stage dependencies are structured to optimize the critical path.
@@ -104,7 +108,24 @@ stages:
           analyzeBuild: true
           buildBenchmarks: true
           numShards: 1
-          skipTesting: true
+          configureTesting: false
+          runTesting: false
+
+  - stage: Configure_Tests
+    dependsOn: []
+    displayName: 'Configure Tests'
+    pool:
+      name: ${{ variables.poolName }}
+      demands: ${{ variables.poolDemands }}
+    jobs:
+      - template: azure-devops/build-and-test.yml
+        parameters:
+          hostArch: x64
+          targetArch: x64
+          targetPlatform: x64
+          numShards: 1
+          buildStl: false
+          runTesting: false
 
   - stage: Test_x64
     dependsOn:
@@ -113,6 +134,7 @@ stages:
       - Build_x86
       - Build_ARM64_Cross
       - Build_ARM64EC_Cross
+      - Configure_Tests
     displayName: 'Test x64'
     pool:
       name: ${{ variables.poolName }}
diff --git a/llvm-project b/llvm-project
index 958cec0ab1b..b725bdba1fa 160000
--- a/llvm-project
+++ b/llvm-project
@@ -1 +1 @@
-Subproject commit 958cec0ab1bbbdc47ea207460de72c5fee24be70
+Subproject commit b725bdba1faf256c725f5fd12c581acb381bf0d3
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 584b4244f2f..1b3bd94e558 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -1,6 +1,8 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+find_package(Python "3.14.0" REQUIRED COMPONENTS Interpreter)
+
 set(STL_BUILD_ROOT "${PROJECT_BINARY_DIR}/out")
 set(STL_SOURCE_DIR "${PROJECT_SOURCE_DIR}")
 set(STL_TEST_OUTPUT_DIR "${CMAKE_CURRENT_BINARY_DIR}")
@@ -23,8 +25,6 @@ add_subdirectory(tr1)
 # chance to add to the config map and test directory global properties.
 add_subdirectory(utils/stl-lit)
 
-find_package(Python "3.14.0" REQUIRED COMPONENTS Interpreter)
-
 if(NOT DEFINED LIT_FLAGS)
     set(LIT_FLAGS "-o" "${CMAKE_CURRENT_BINARY_DIR}/test_results.json")
 endif()
diff --git a/tests/libcxx/CMakeLists.txt b/tests/libcxx/CMakeLists.txt
index cdcc763ff3d..bb1a94e5550 100644
--- a/tests/libcxx/CMakeLists.txt
+++ b/tests/libcxx/CMakeLists.txt
@@ -1,6 +1,11 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+execute_process(
+  COMMAND "${Python_EXECUTABLE}" "${STL_SOURCE_DIR}/tools/scripts/check_libcxx_paths.py"
+  COMMAND_ERROR_IS_FATAL ANY
+)
+
 set(LIBCXX_ENVLST "${CMAKE_CURRENT_SOURCE_DIR}/usual_matrix.lst")
 set(LIBCXX_EXPECTED_RESULTS "${CMAKE_CURRENT_SOURCE_DIR}/expected_results.txt")
 set(LIBCXX_TEST_OUTPUT_DIR "${STL_TEST_OUTPUT_DIR}/libcxx")
diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index 23dcd2bbca2..88ffdfa720a 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -61,9 +61,6 @@ std/language.support/support.exception/except.nested/ctor_default.pass.cpp:2 SKI
 # SKIPPED because this is ARM64EC-specific.
 std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp:2 SKIPPED
 
-# LLVM-160627: [libc++][test] Guard non-guaranteed implicit-lifetime-ness cases with _LIBCPP_VERSION
-std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp:2 FAIL
-
 # Non-Standard regex behavior.
 # "It seems likely that the test is still non-conforming due to how libc++ handles the 'w' character class."
 std/re/re.traits/lookup_classname.pass.cpp FAIL
@@ -574,8 +571,10 @@ std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporar
 std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp:1 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp:0 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp:1 FAIL
-std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp:0 FAIL
-std/utilities/tuple/tuple.tuple/tuple.cnstr/PR20855_tuple_ref_binding_diagnostics.pass.cpp:1 FAIL
+
+# P2835R7 atomic_ref::address()
+# Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
+std/atomics/atomics.ref/address.pass.cpp FAIL
 
 # P2944R3 Comparisons For reference_wrapper
 # Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
@@ -583,9 +582,23 @@ std/utilities/function.objects/refwrap/refwrap.comparisons/compare.three_way.ref
 std/utilities/function.objects/refwrap/refwrap.comparisons/compare.three_way.refwrap.refwrap_const.pass.cpp FAIL
 std/utilities/function.objects/refwrap/refwrap.comparisons/compare.three_way.refwrap.refwrap.pass.cpp FAIL
 
+# P2988R12 optional<T&>
+# Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
+std/utilities/optional/optional.object/optional.object.ctor/ref_t.pass.cpp FAIL
+
+# P3044R2 basic_string::subview()
+# Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
+std/strings/basic.string/string.ops/string_substr/subview.pass.cpp FAIL
+std/strings/string.view/string.view.ops/subview.pass.cpp FAIL
+
+# P3060R3 views::indices
+# Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
+std/ranges/range.factories/range.iota.view/indices.pass.cpp FAIL
+
 # P3168R2 std::optional Range Support
 # Add 'std-at-least-c++26' to tests/utils/stl/test/tests.py when beginning work on C++26.
 std/utilities/optional/optional.iterator/begin.pass.cpp FAIL
+std/utilities/optional/optional.iterator/borrowed_range.compile.pass.cpp FAIL
 std/utilities/optional/optional.iterator/end.pass.cpp FAIL
 std/utilities/optional/optional.iterator/iterator.pass.cpp FAIL
 
@@ -640,10 +653,6 @@ std/utilities/variant/variant.relops/three_way.pass.cpp:1 FAIL
 std/algorithms/robust_re_difference_type.compile.pass.cpp:0 FAIL
 std/algorithms/robust_re_difference_type.compile.pass.cpp:1 FAIL
 
-# DevCom-10026599 VSO-1532879: conditional expression has two different types
-std/concepts/concepts.compare/concept.equalitycomparable/equality_comparable_with.compile.pass.cpp:0 FAIL
-std/concepts/concepts.compare/concept.equalitycomparable/equality_comparable_with.compile.pass.cpp:1 FAIL
-
 # DevCom-10439137 VSO-1869865: Discarded id-expression causes unnecessary reading
 std/containers/sequences/array/array.cons/initialization.pass.cpp:0 FAIL
 std/containers/sequences/array/array.cons/initialization.pass.cpp:1 FAIL
@@ -819,21 +828,13 @@ std/input.output/syncstream/syncbuf/syncstream.syncbuf.cons/dtor.pass.cpp FAIL
 std/input.output/syncstream/syncbuf/syncstream.syncbuf.members/emit.pass.cpp FAIL
 
 # GH-5393: <regex>: What names can and should regex_traits::lookup_collatename() recognize?
-std/re/re.alg/re.alg.match/awk.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.match/awk.pass.cpp FAIL
-std/re/re.alg/re.alg.match/basic.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.match/basic.pass.cpp FAIL
-std/re/re.alg/re.alg.match/ecma.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.match/ecma.pass.cpp FAIL
-std/re/re.alg/re.alg.match/extended.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.match/extended.pass.cpp FAIL
-std/re/re.alg/re.alg.search/awk.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.search/awk.pass.cpp FAIL
-std/re/re.alg/re.alg.search/basic.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.search/basic.pass.cpp FAIL
-std/re/re.alg/re.alg.search/ecma.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.search/ecma.pass.cpp FAIL
-std/re/re.alg/re.alg.search/extended.locale.pass.cpp FAIL
 std/re/re.alg/re.alg.search/extended.pass.cpp FAIL
 std/re/re.traits/lookup_collatename.pass.cpp FAIL
 
@@ -896,11 +897,15 @@ std/thread/thread.threads/thread.thread.this/sleep_until.pass.cpp SKIPPED
 std/thread/thread.semaphore/timed.pass.cpp SKIPPED
 
 # "This is technically flaky" comments indicate tests with timing assumptions.
-# These tests have failed in practice, see VSO-2321213 and VSO-2416940.
+# These tests have failed in practice, see VSO-2321213, VSO-2416940, and GH-5899.
 std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_for.pass.cpp SKIPPED
 std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared_for.pass.cpp SKIPPED
 std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared_until.pass.cpp SKIPPED
 std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_until.pass.cpp SKIPPED
+std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock_for.pass.cpp SKIPPED
+std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.class/try_lock_until.pass.cpp SKIPPED
+std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock_for.pass.cpp SKIPPED
+std/thread/thread.mutex/thread.mutex.requirements/thread.timedmutex.requirements/thread.timedmutex.recursive/try_lock_until.pass.cpp SKIPPED
 
 # Not analyzed, likely bogus tests. Various assertions, probably POSIX assumptions.
 std/diagnostics/syserr/syserr.syserr/syserr.syserr.members/ctor_error_code_const_char_pointer.pass.cpp FAIL
@@ -1497,17 +1502,16 @@ std/utilities/function.objects/refwrap/common_reference.compile.pass.cpp:1 FAIL
 std/utilities/meta/meta.trans/meta.trans.other/common_reference.compile.pass.cpp:0 FAIL
 std/utilities/meta/meta.trans/meta.trans.other/common_reference.compile.pass.cpp:1 FAIL
 
-# Not analyzed.
-# MSVC emits truncation warnings, which will be partially addressed by GH-5562.
-# Clang asserts `allocated_ == 0 || allocated_ >= i` due to the container proxy object.
-std/strings/basic.string/string.capacity/deallocate_size.pass.cpp FAIL
-
 # Not analyzed. MSVC emits warning C4267: 'argument': conversion from 'size_t' to 'unsigned char', possible loss of data
 std/algorithms/alg.modifying.operations/alg.copy/copy_backward.pass.cpp:0 FAIL
 std/algorithms/alg.modifying.operations/alg.copy/copy_backward.pass.cpp:1 FAIL
 std/algorithms/alg.modifying.operations/alg.copy/copy.pass.cpp:0 FAIL
 std/algorithms/alg.modifying.operations/alg.copy/copy.pass.cpp:1 FAIL
 
+# Not analyzed. MSVC emits warning C4242: 'argument': conversion from 'int' to 'char', possible loss of data
+std/input.output/file.streams/fstreams/filebuf.virtuals/xsputn.pass.cpp:0 FAIL
+std/input.output/file.streams/fstreams/filebuf.virtuals/xsputn.pass.cpp:1 FAIL
+
 
 # *** XFAILS WHICH PASS ***
 # These tests contain `// XFAIL: msvc` comments, which accurately describe runtime failures for x86 and x64.
diff --git a/tests/std/CMakeLists.txt b/tests/std/CMakeLists.txt
index 5aa4a346bf9..40bb8eb7b6a 100644
--- a/tests/std/CMakeLists.txt
+++ b/tests/std/CMakeLists.txt
@@ -1,6 +1,11 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+execute_process(
+  COMMAND "${Python_EXECUTABLE}" "${STL_SOURCE_DIR}/tools/scripts/check_test_lst_paths.py" "${CMAKE_CURRENT_SOURCE_DIR}"
+  COMMAND_ERROR_IS_FATAL ANY
+)
+
 set(STD_EXPECTED_RESULTS "${CMAKE_CURRENT_SOURCE_DIR}/expected_results.txt")
 set(STD_TEST_OUTPUT_DIR "${STL_TEST_OUTPUT_DIR}/std")
 
diff --git a/tests/std/test.lst b/tests/std/test.lst
index 8a583d890a5..c44a4197217 100644
--- a/tests/std/test.lst
+++ b/tests/std/test.lst
@@ -1,6 +1,12 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+# CUDA is not available in the MSVC-internal test harness:
+# tests\GH_000639_nvcc_include_all
+
+# Needs special machinery to work in the MSVC-internal test harness, not yet implemented:
+# tests\GH_002094_cpp_core_guidelines
+
 tests\Dev08_496675_iostream_int_reading
 tests\Dev08_527068_scl_no_exceptions
 tests\Dev08_563686_ostream
@@ -207,8 +213,6 @@ tests\GH_002030_asan_annotate_vector
 tests\GH_002039_byte_is_not_trivially_swappable
 tests\GH_002045_put_time_changes_errno
 tests\GH_002058_debug_iterator_race
-# Needs special machinery to work in the MSVC-internal test harness, not yet implemented:
-# tests\GH_002094_cpp_core_guidelines
 tests\GH_002120_streambuf_seekpos_and_seekoff
 tests\GH_002168_regex_overflow
 tests\GH_002206_unreserved_names
@@ -417,13 +421,13 @@ tests\P0784R7_library_support_for_more_constexpr_containers
 tests\P0798R8_monadic_operations_for_std_optional
 tests\P0811R3_midpoint_lerp
 tests\P0881R7_stacktrace
+tests\P0896R4_and_P1614R2_comparisons
 tests\P0896R4_common_iterator
 tests\P0896R4_common_iterator_death
 tests\P0896R4_counted_iterator
 tests\P0896R4_counted_iterator_death
 tests\P0896R4_istream_view
 tests\P0896R4_istream_view_death
-tests\P0896R4_P1614R2_comparisons
 tests\P0896R4_ranges_alg_adjacent_find
 tests\P0896R4_ranges_alg_all_of
 tests\P0896R4_ranges_alg_any_of
diff --git a/tests/std/tests/P0896R4_P1614R2_comparisons/env.lst b/tests/std/tests/P0896R4_and_P1614R2_comparisons/env.lst
similarity index 100%
rename from tests/std/tests/P0896R4_P1614R2_comparisons/env.lst
rename to tests/std/tests/P0896R4_and_P1614R2_comparisons/env.lst
diff --git a/tests/std/tests/P0896R4_P1614R2_comparisons/test.cpp b/tests/std/tests/P0896R4_and_P1614R2_comparisons/test.cpp
similarity index 100%
rename from tests/std/tests/P0896R4_P1614R2_comparisons/test.cpp
rename to tests/std/tests/P0896R4_and_P1614R2_comparisons/test.cpp
diff --git a/tests/tr1/CMakeLists.txt b/tests/tr1/CMakeLists.txt
index b09e61bbf06..9bedec5f2f4 100644
--- a/tests/tr1/CMakeLists.txt
+++ b/tests/tr1/CMakeLists.txt
@@ -1,6 +1,11 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+execute_process(
+  COMMAND "${Python_EXECUTABLE}" "${STL_SOURCE_DIR}/tools/scripts/check_test_lst_paths.py" "${CMAKE_CURRENT_SOURCE_DIR}"
+  COMMAND_ERROR_IS_FATAL ANY
+)
+
 set(TR1_EXPECTED_RESULTS "${CMAKE_CURRENT_SOURCE_DIR}/expected_results.txt")
 set(TR1_TEST_OUTPUT_DIR "${STL_TEST_OUTPUT_DIR}/tr1")
 
diff --git a/tools/scripts/check_libcxx_paths.py b/tools/scripts/check_libcxx_paths.py
index 93a4f34b351..7113bf16d67 100644
--- a/tools/scripts/check_libcxx_paths.py
+++ b/tools/scripts/check_libcxx_paths.py
@@ -13,28 +13,24 @@
 
     # Use the location of this script to find the base of the repo.
     absolute_repo_path = Path(sys.argv[0]).absolute().parents[2]
+    expected_results_txt = "tests/libcxx/expected_results.txt"
 
     # Tests can be mentioned multiple times for different configurations.
     # Build up a unique set before checking for existence.
-    unique_tests = set()
+    with open(absolute_repo_path / expected_results_txt) as file:
+        stripped_lines = [line.strip() for line in file]
 
-    with open(absolute_repo_path / "tests/libcxx/expected_results.txt") as file:
-        for line in map(lambda x: x.strip(), file):
-            if line and not line.startswith("#"): # Ignore empty lines and comments.
-                unique_tests.add(re.sub(r"(:\d+)? (FAIL|SKIPPED)$", "", line))
+    filtered_lines = [s for s in stripped_lines if s and not s.startswith("#")] # Ignore empty lines and comments.
+    config_rgx = re.compile(r"(:\d+)? (FAIL|SKIPPED)$")
+    unique_tests = {config_rgx.sub("", line) for line in filtered_lines}
 
     # Build up a list of nonexistent tests so they can be printed in sorted order.
-    nonexistent_tests = []
-
-    for str in unique_tests:
-        if not (absolute_repo_path / "llvm-project/libcxx/test" / str).is_file():
-            nonexistent_tests.append(str)
+    absolute_libcxx_test = absolute_repo_path / "llvm-project/libcxx/test"
+    nonexistent_tests = [str for str in unique_tests if not (absolute_libcxx_test / str).is_file()]
 
     if nonexistent_tests:
-        print(f"Failure, found {len(nonexistent_tests)} nonexistent test paths:")
-        nonexistent_tests.sort()
-        for str in nonexistent_tests:
-            print(f"{str}")
+        print(f"Failure: {expected_results_txt} contains {len(nonexistent_tests)} nonexistent tests:", file=sys.stderr)
+        for str in sorted(nonexistent_tests):
+            print(f"{str}", file=sys.stderr)
+        print(f"##vso[task.logissue type=error]{expected_results_txt} failed validation, see log.", file=sys.stderr)
         sys.exit(1)
-
-    print("Success, all test paths exist.")
diff --git a/tools/scripts/check_test_lst_paths.py b/tools/scripts/check_test_lst_paths.py
new file mode 100644
index 00000000000..e308139258b
--- /dev/null
+++ b/tools/scripts/check_test_lst_paths.py
@@ -0,0 +1,74 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+# This script checks tests/std/test.lst (and tr1) for duplicate, missing, nonexistent, and unsorted test paths.
+
+from pathlib import Path
+import sys
+
+def is_nonempty_dir(p: Path) -> bool:
+    return p.is_dir() and any(p.iterdir())
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        sys.exit(f"Usage: python {sys.argv[0]} tests/std-OR-tr1")
+
+    absolute_base = Path(sys.argv[1]).absolute()
+    absolute_tests = absolute_base / "tests"
+    absolute_test_lst = absolute_base / "test.lst"
+    relative_test_lst = absolute_test_lst.relative_to(absolute_test_lst.parents[2])
+
+    with open(absolute_test_lst) as file:
+        stripped_lines = [line.strip() for line in file]
+
+    filtered_lines = [s for s in stripped_lines if s and not s.startswith("#")] # Ignore empty lines and comments.
+
+    unique_tests = set()
+    duplicate_tests = set()
+    for line in filtered_lines:
+        if line in unique_tests:
+            duplicate_tests.add(line) # Repeatedly duplicated tests will be reported only once.
+        else:
+            unique_tests.add(line)
+
+    existing_tests = {fR"tests\{p.name}" for p in absolute_tests.iterdir() if is_nonempty_dir(p)}
+
+    commented_tests = { # These tests are commented out. Avoid reporting them as missing.
+        R"tests\GH_000639_nvcc_include_all",
+        R"tests\GH_002094_cpp_core_guidelines",
+    }
+
+    missing_tests = existing_tests - commented_tests - unique_tests
+
+    nonexistent_tests = [str for str in unique_tests if not is_nonempty_dir(absolute_base / str)]
+
+    failed = False
+
+    if duplicate_tests:
+        failed = True
+        print(f"Failure: {relative_test_lst} contains {len(duplicate_tests)} duplicate tests:", file=sys.stderr)
+        for str in sorted(duplicate_tests):
+            print(f"{str}", file=sys.stderr)
+
+    if missing_tests:
+        failed = True
+        print(f"Failure: {relative_test_lst} is missing {len(missing_tests)} tests:", file=sys.stderr)
+        for str in sorted(missing_tests):
+            print(f"{str}", file=sys.stderr)
+
+    if nonexistent_tests:
+        failed = True
+        print(f"Failure: {relative_test_lst} contains {len(nonexistent_tests)} nonexistent tests:", file=sys.stderr)
+        for str in sorted(nonexistent_tests):
+            print(f"{str}", file=sys.stderr)
+
+    for i in range(len(filtered_lines) - 1): # If filtered_lines is empty, range(-1) is empty.
+        if filtered_lines[i] > filtered_lines[i + 1]: # Use greater-than to avoid reporting adjacent duplicates.
+            failed = True
+            print(f"Failure: {relative_test_lst} isn't sorted, starting with:", file=sys.stderr)
+            print(f"{filtered_lines[i + 1]}", file=sys.stderr)
+            break # Report only the first unsorted line.
+
+    if failed:
+        print(f"##vso[task.logissue type=error]{relative_test_lst} failed validation, see log.", file=sys.stderr)
+        sys.exit(1)