diff --git a/lldb/include/lldb/Utility/ReproducerInstrumentation.h b/lldb/include/lldb/Utility/ReproducerInstrumentation.h
--- a/lldb/include/lldb/Utility/ReproducerInstrumentation.h
+++ b/lldb/include/lldb/Utility/ReproducerInstrumentation.h
@@ -841,6 +841,10 @@
 
   bool ShouldCapture() { return m_local_boundary; }
 
+  /// Mark the current thread as a private thread and pretend that everything
+  /// on this thread is behind happening behind the API boundary.
+  static void PrivateThread() { g_global_boundary = true; }
+
 private:
   template <typename T> friend struct replay;
   void UpdateBoundary() {
@@ -868,7 +872,7 @@
   bool m_result_recorded;
 
   /// Whether we're currently across the API boundary.
-  static bool g_global_boundary;
+  static thread_local bool g_global_boundary;
 };
 
 /// To be used as the "Runtime ID" of a constructor. It also invokes the
diff --git a/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp b/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
--- a/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
+++ b/lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp
@@ -33,6 +33,7 @@
 #include "lldb/Interpreter/CommandReturnObject.h"
 #include "lldb/Target/Thread.h"
 #include "lldb/Target/ThreadPlan.h"
+#include "lldb/Utility/ReproducerInstrumentation.h"
 #include "lldb/Utility/Timer.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -437,6 +438,7 @@
     : ScriptInterpreterLocker(),
       m_teardown_session((on_leave & TearDownSession) == TearDownSession),
       m_python_interpreter(py_interpreter) {
+  repro::Recorder::PrivateThread();
   DoAcquireLock();
   if ((on_entry & InitSession) == InitSession) {
     if (!DoInitSession(on_entry, in, out, err)) {
diff --git a/lldb/source/Utility/ReproducerInstrumentation.cpp b/lldb/source/Utility/ReproducerInstrumentation.cpp
--- a/lldb/source/Utility/ReproducerInstrumentation.cpp
+++ b/lldb/source/Utility/ReproducerInstrumentation.cpp
@@ -227,4 +227,4 @@
   return g_instrumentation_data;
 }
 
-bool lldb_private::repro::Recorder::g_global_boundary;
+thread_local bool lldb_private::repro::Recorder::g_global_boundary = false;