diff --git a/include/swift/AST/ModuleDependencies.h b/include/swift/AST/ModuleDependencies.h
index fe42ade6a48..ac95c56461e 100644
--- a/include/swift/AST/ModuleDependencies.h
+++ b/include/swift/AST/ModuleDependencies.h
@@ -1093,6 +1093,13 @@ public:
   /// Allocate string inside ScanningService.
   StringRef save(StringRef str);
 
+  /// Get clang scanning service.
+  const clang::tooling::dependencies::DependencyScanningService &
+  getClangScanningService() const {
+    assert(ClangScanningService);
+    return *ClangScanningService;
+  }
+
 private:
   /// Enforce clients not being allowed to query this cache directly, it must be
   /// wrapped in an instance of `ModuleDependenciesCache`.
diff --git a/include/swift/DependencyScan/ModuleDependencyScanner.h b/include/swift/DependencyScan/ModuleDependencyScanner.h
index 26b7b29331f..1996753313e 100644
--- a/include/swift/DependencyScan/ModuleDependencyScanner.h
+++ b/include/swift/DependencyScan/ModuleDependencyScanner.h
@@ -315,8 +315,6 @@ private:
                           const SILOptions &SILOptions,
                           ASTContext &ScanASTContext,
                           DependencyTracker &DependencyTracker,
-                          std::shared_ptr<llvm::cas::ObjectStore> CAS,
-                          std::shared_ptr<llvm::cas::ActionCache> ActionCache,
                           DiagnosticEngine &Diagnostics, bool ParallelScan,
                           bool EmitScanRemarks);
   llvm::Error initializeWorkerClangScanningTool();
diff --git a/lib/AST/ModuleDependencies.cpp b/lib/AST/ModuleDependencies.cpp
index c0cd6762f66..1baaabd0cc0 100644
--- a/lib/AST/ModuleDependencies.cpp
+++ b/lib/AST/ModuleDependencies.cpp
@@ -655,7 +655,7 @@ swift::dependencies::registerBackDeployLibraries(
 
 bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
     CompilerInstance &Instance) {
-  if (!Instance.getInvocation().getCASOptions().EnableCaching)
+  if (!Instance.getInvocation().requiresCAS())
     return false;
 
   if (CASConfig) {
diff --git a/lib/DependencyScan/DependencyScanningTool.cpp b/lib/DependencyScan/DependencyScanningTool.cpp
index 3c77dce46de..e60152b3334 100644
--- a/lib/DependencyScan/DependencyScanningTool.cpp
+++ b/lib/DependencyScan/DependencyScanningTool.cpp
@@ -390,6 +390,12 @@ llvm::ErrorOr<ScanQueryContext> DependencyScanningTool::createScanQueryContext(
     if (std::error_code EC = Invocation.getError())
       return EC;
 
+    // Setup the CAS instance from scanning service if applicable.
+    if (Invocation->requiresCAS())
+      Instance->setSharedCASInstances(
+          ScanningService->getClangScanningService().getCAS(),
+          ScanningService->getClangScanningService().getActionCache());
+
     // Setup the instance
     std::string InstanceSetupError;
     if (Instance->setup(*Invocation, InstanceSetupError))
diff --git a/lib/DependencyScan/ModuleDependencyScanner.cpp b/lib/DependencyScan/ModuleDependencyScanner.cpp
index dbce6bfb6fb..586c439c428 100644
--- a/lib/DependencyScan/ModuleDependencyScanner.cpp
+++ b/lib/DependencyScan/ModuleDependencyScanner.cpp
@@ -218,6 +218,12 @@ ModuleDependencyScanningWorker::ModuleDependencyScanningWorker(
           getClangScanningFS(globalScanningService, CAS, ScanASTContext)),
       CAS(CAS), ActionCache(ActionCache),
       diagnosticReporter(DiagnosticReporter) {
+  assert(globalScanningService.ClangScanningService->getCAS() == CAS &&
+         "Need to be the same CAS instance");
+  assert(globalScanningService.ClangScanningService->getActionCache() ==
+             ActionCache &&
+         "Need to be the same ActionCache instance");
+
   // Instantiate a worker-specific diagnostic engine and copy over
   // the scanner's diagnostic consumers (expected to be thread-safe).
   workerDiagnosticEngine = std::make_unique<DiagnosticEngine>(ScanASTContext.SourceMgr);
@@ -534,7 +540,6 @@ ModuleDependencyScanner::create(SwiftDependencyScanningService &service,
       std::unique_ptr<ModuleDependencyScanner>(new ModuleDependencyScanner(
           service, cache, instance->getInvocation(), instance->getSILOptions(),
           instance->getASTContext(), *instance->getDependencyTracker(),
-          instance->getSharedCASInstance(), instance->getSharedCacheInstance(),
           instance->getDiags(),
           instance->getInvocation().getFrontendOptions().ParallelDependencyScan,
           instance->getInvocation()
@@ -560,24 +565,22 @@ ModuleDependencyScanner::ModuleDependencyScanner(
     ModuleDependenciesCache &Cache,
     const CompilerInvocation &ScanCompilerInvocation,
     const SILOptions &SILOptions, ASTContext &ScanASTContext,
-    swift::DependencyTracker &DependencyTracker,
-    std::shared_ptr<llvm::cas::ObjectStore> CAS,
-    std::shared_ptr<llvm::cas::ActionCache> ActionCache,
-    DiagnosticEngine &Diagnostics, bool ParallelScan,
-    bool EmitScanRemarks)
+    swift::DependencyTracker &DependencyTracker, DiagnosticEngine &Diagnostics,
+    bool ParallelScan, bool EmitScanRemarks)
     : ScanCompilerInvocation(ScanCompilerInvocation),
       ScanASTContext(ScanASTContext),
       ScanDiagnosticReporter(Diagnostics, EmitScanRemarks),
       ModuleOutputPath(ScanCompilerInvocation.getFrontendOptions()
-                       .ExplicitModulesOutputPath),
+                           .ExplicitModulesOutputPath),
       SDKModuleOutputPath(ScanCompilerInvocation.getFrontendOptions()
-                          .ExplicitSDKModulesOutputPath),
+                              .ExplicitSDKModulesOutputPath),
       DependencyCache(Cache),
       NumThreads(ParallelScan
                      ? llvm::hardware_concurrency().compute_thread_count()
                      : 1),
-      ScanningThreadPool(llvm::hardware_concurrency(NumThreads)), CAS(CAS),
-      ActionCache(ActionCache) {
+      ScanningThreadPool(llvm::hardware_concurrency(NumThreads)),
+      CAS(ScanningService.ClangScanningService->getCAS()),
+      ActionCache(ScanningService.ClangScanningService->getActionCache()) {
   // Setup prefix mapping.
   auto &ScannerPrefixMapper =
       ScanCompilerInvocation.getSearchPathOptions().ScannerPrefixMapper;
diff --git a/test/CAS/swift-scan-test-multithread.swift b/test/CAS/swift-scan-test-multithread.swift
new file mode 100644
index 00000000000..30de06458cc
--- /dev/null
+++ b/test/CAS/swift-scan-test-multithread.swift
@@ -0,0 +1,39 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+/// Test parallel dependency scanning from libSwiftScan APIs.
+ // RUN: %swift-scan-test -action scan_dependency -cas-path %t/cas -threads 5 -- \
+// RUN:   %target-swift-frontend -scan-dependencies -target arm64-apple-macos26 -module-name Test -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %t/main.swift -o %t/deps.json -sdk %sdk -swift-version 5 -cache-compile-job -cas-path %t/cas -I %t/include > %t/deps.json
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json A | %FileCheck %s --check-prefix=INTERFACE_A
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:B | %FileCheck %s --check-prefix=PCM_B
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json Test | %FileCheck %s --check-prefix=TEST
+
+// INTERFACE_A: -frontend
+// INTERFACE_A: -compile-module-from-interface
+
+// PCM_B: -frontend
+// PCM_B: -emit-pcm
+
+// TEST: -direct-clang-cc1-module-build
+
+//--- include/module.modulemap
+module B {
+  header "B.h"
+  export *
+}
+
+//--- include/B.h
+void notused(void);
+
+//--- include/A.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name A -O -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -user-module-version 1.0
+import B
+
+public struct A {}
+
+//--- main.swift
+import A