diff --git a/swift/internal/compiling.bzl b/swift/internal/compiling.bzl
index fba2971d4..5690a599e 100644
--- a/swift/internal/compiling.bzl
+++ b/swift/internal/compiling.bzl
@@ -60,6 +60,7 @@ load(
     "SWIFT_FEATURE_USE_C_MODULES",
     "SWIFT_FEATURE_USE_GLOBAL_INDEX_STORE",
     "SWIFT_FEATURE_USE_GLOBAL_MODULE_CACHE",
+    "SWIFT_FEATURE_USE_HOST_NUM_THREADS",
     "SWIFT_FEATURE_VFSOVERLAY",
     "SWIFT_FEATURE__NUM_THREADS_0_IN_SWIFTCOPTS",
     "SWIFT_FEATURE__WMO_IN_SWIFTCOPTS",
@@ -767,6 +768,16 @@ def compile_action_configs(
             ],
             not_features = [SWIFT_FEATURE__NUM_THREADS_0_IN_SWIFTCOPTS],
         ),
+        swift_toolchain_config.action_config(
+            actions = [
+                swift_action_names.COMPILE,
+                swift_action_names.DERIVE_FILES,
+            ],
+            configurators = [_wmo_host_thread_count_configurator],
+            features = [
+                [SWIFT_FEATURE_USE_HOST_NUM_THREADS, SWIFT_FEATURE__WMO_IN_SWIFTCOPTS],
+            ],
+        ),
         swift_toolchain_config.action_config(
             actions = [
                 swift_action_names.COMPILE,
@@ -1385,6 +1396,11 @@ def _wmo_thread_count_configurator(should_check_flags, prerequisites, args):
         # Force threaded mode for WMO builds.
         args.add("-num-threads", str(_DEFAULT_WMO_THREAD_COUNT))
 
+def _wmo_host_thread_count_configurator(prerequisites, args):
+    """Sets num-threads to number of threads on the host.
+    """
+    args.add("-Xwrapped-swift=-use-host-num-threads")
+
 def _is_wmo_manually_requested(user_compile_flags):
     """Returns `True` if a WMO flag is in the given list of compiler flags.
 
diff --git a/swift/internal/feature_names.bzl b/swift/internal/feature_names.bzl
index 318235d0c..c3e964126 100644
--- a/swift/internal/feature_names.bzl
+++ b/swift/internal/feature_names.bzl
@@ -266,3 +266,6 @@ SWIFT_FEATURE__WMO_IN_SWIFTCOPTS = "swift._wmo_in_swiftcopts"
 # were passed on the command line using `--swiftcopt`. Users should never
 # manually enable, disable, or query this feature.
 SWIFT_FEATURE__NUM_THREADS_0_IN_SWIFTCOPTS = "swift._num_threads_0_in_swiftcopts"
+
+# If enabled, it passes the number of threads that the host has
+SWIFT_FEATURE_USE_HOST_NUM_THREADS = "swift.use_host_num_threads"
diff --git a/tools/worker/swift_runner.cc b/tools/worker/swift_runner.cc
index 41068581c..6dadbc5c1 100644
--- a/tools/worker/swift_runner.cc
+++ b/tools/worker/swift_runner.cc
@@ -14,6 +14,9 @@
 
 #include "tools/worker/swift_runner.h"
 
+#include <sys/sysctl.h>
+#include <sys/types.h>
+
 #include <fstream>
 
 #include "tools/common/bazel_substitutions.h"
@@ -102,7 +105,7 @@ static bool StripPrefix(const std::string &prefix, std::string &str) {
 
 SwiftRunner::SwiftRunner(const std::vector<std::string> &args,
                          bool force_response_file)
-    : force_response_file_(force_response_file) {
+    : force_response_file_(force_response_file), use_host_num_threads_(false) {
   args_ = ProcessArguments(args);
 }
 
@@ -257,6 +260,26 @@ bool SwiftRunner::ProcessPossibleResponseFile(
   return changed;
 }
 
+static int GetNumCPU() {
+  int sysctlarg[4];
+  int numCPU;
+  std::size_t len = sizeof(numCPU);
+
+  // set the sysctlarg for hw.ncpu
+  sysctlarg[0] = CTL_HW;
+  sysctlarg[1] = HW_AVAILCPU;
+
+  // Gets NCPU from sysctl
+  sysctl(sysctlarg, 2, &numCPU, &len, NULL, 0);
+
+  if (numCPU < 1) {
+    sysctlarg[1] = HW_NCPU;
+    sysctl(sysctlarg, 2, &numCPU, &len, NULL, 0);
+    if (numCPU < 1) numCPU = 1;
+  }
+  return numCPU;
+}
+
 template <typename Iterator>
 bool SwiftRunner::ProcessArgument(
     Iterator &itr, const std::string &arg,
@@ -318,6 +341,14 @@ bool SwiftRunner::ProcessArgument(
         ++itr;
         new_arg = output_file_map_path_;
         changed = true;
+      } else if (use_host_num_threads_ && arg == "-num-threads") {
+        consumer("-num-threads");
+
+        // If we're using the number of threads on the host, set this value to
+        // the NumCPU.
+        ++itr;
+        new_arg = std::to_string(GetNumCPU());
+        changed = true;
       }
 
       // Apply any other text substitutions needed in the argument (i.e., for
@@ -347,6 +378,8 @@ std::vector<std::string> SwiftRunner::ParseArguments(Iterator itr) {
         global_index_store_import_path_ = arg;
       } else if (StripPrefix("-generated-header-rewriter=", arg)) {
         generated_header_rewriter_path_ = arg;
+      } else if (StripPrefix("-use-host-num-threads", arg)) {
+        use_host_num_threads_ = true;
       }
     } else {
       if (arg == "-output-file-map") {
diff --git a/tools/worker/swift_runner.h b/tools/worker/swift_runner.h
index ad5389576..231ca231c 100644
--- a/tools/worker/swift_runner.h
+++ b/tools/worker/swift_runner.h
@@ -146,6 +146,9 @@ class SwiftRunner {
   // `-index-store-path`. After running `swiftc` `index-import` copies relevant
   // index outputs into the `index_store_path` to integrate outputs with Bazel.
   std::string global_index_store_import_path_;
+
+  // If the worker should set num-threads to number of threads on the host.
+  bool use_host_num_threads_;
 };
 
 #endif  // BUILD_BAZEL_RULES_SWIFT_TOOLS_WORKER_SWIFT_RUNNER_H_