diff --git a/example_trainer/vllm_patching/patched_gpu_runner.py b/example_trainer/vllm_patching/patched_gpu_runner.py
index 3c124598..7631683d 100644
--- a/example_trainer/vllm_patching/patched_gpu_runner.py
+++ b/example_trainer/vllm_patching/patched_gpu_runner.py
@@ -267,7 +267,13 @@ def _create_patched_runner(BaseRunner: type) -> type:
                 traceback.print_exc()
         
         def _spawn_weight_updater(self) -> None:
-            """Spawn the daemon process for receiving weight updates."""
+            """Start the weight updater as a background thread.
+            
+            Note: We use threading instead of multiprocessing because vLLM's
+            worker processes are daemons, and daemons cannot spawn child processes.
+            """
+            import threading
+            
             print("[vLLM Patch] _spawn_weight_updater() called", flush=True)
             
             try:
@@ -302,14 +308,10 @@ def _create_patched_runner(BaseRunner: type) -> type:
             except Exception:
                 gpu_id = tp_rank
             
-            print(f"[vLLM Patch] Spawning weight updater: tp_rank={tp_rank}, gpu={gpu_id}", flush=True)
+            print(f"[vLLM Patch] Starting weight updater thread: tp_rank={tp_rank}, gpu={gpu_id}", flush=True)
             
-            # Spawn daemon process
-            print("[vLLM Patch] Creating spawn context...", flush=True)
-            ctx = mp.get_context("spawn")
-            
-            print("[vLLM Patch] Creating Process...", flush=True)
-            self.weight_updater_process = ctx.Process(
+            # Start as a daemon thread (threads CAN be started from daemon processes)
+            self.weight_updater_thread = threading.Thread(
                 target=weight_updater_process,
                 args=(
                     state_dict,
@@ -320,12 +322,13 @@ def _create_patched_runner(BaseRunner: type) -> type:
                     gpu_id,
                 ),
                 daemon=True,
+                name=f"WeightUpdater_TP{tp_rank}",
             )
             
-            print("[vLLM Patch] Starting daemon process...", flush=True)
-            self.weight_updater_process.start()
+            print("[vLLM Patch] Starting thread...", flush=True)
+            self.weight_updater_thread.start()
             
-            print(f"[vLLM Patch] ✓ Weight updater daemon started (PID: {self.weight_updater_process.pid})", flush=True)
+            print(f"[vLLM Patch] ✓ Weight updater thread started (name: {self.weight_updater_thread.name})", flush=True)
     
     # Set proper class name
     PatchedGPUModelRunner.__name__ = "PatchedGPUModelRunner"