diff --git a/invokeai/app/services/config/config_default.py b/invokeai/app/services/config/config_default.py
index 39dc1fe83b..895008b753 100644
--- a/invokeai/app/services/config/config_default.py
+++ b/invokeai/app/services/config/config_default.py
@@ -110,7 +110,7 @@ class InvokeAIAppConfig(BaseSettings):
         force_tiled_decode: Whether to enable tiled VAE decode (reduces memory consumption with some performance penalty).
         pil_compress_level: The compress_level setting of PIL.Image.save(), used for PNG encoding. All settings are lossless. 0 = no compression, 1 = fastest with slightly larger filesize, 9 = slowest with smallest filesize. 1 is typically the best setting.
         max_queue_size: Maximum number of items in the session queue.
-        max_threads: Maximum number of session queue execution threads.
+        max_threads: Maximum number of session queue execution threads. Autocalculated from number of GPUs if not set.
         allow_nodes: List of nodes to allow. Omit to allow all.
         deny_nodes: List of nodes to deny. Omit to deny none.
         node_cache_size: How many cached nodes to keep in memory.
@@ -182,7 +182,7 @@ class InvokeAIAppConfig(BaseSettings):
     force_tiled_decode:            bool = Field(default=False,              description="Whether to enable tiled VAE decode (reduces memory consumption with some performance penalty).")
     pil_compress_level:             int = Field(default=1,                  description="The compress_level setting of PIL.Image.save(), used for PNG encoding. All settings are lossless. 0 = no compression, 1 = fastest with slightly larger filesize, 9 = slowest with smallest filesize. 1 is typically the best setting.")
     max_queue_size:                 int = Field(default=10000, gt=0,        description="Maximum number of items in the session queue.")
-    max_threads:                    int = Field(default=4,                  description="Maximum number of session queue execution threads.")
+    max_threads:          Optional[int] = Field(default=None,               description="Maximum number of session queue execution threads. Autocalculated from number of GPUs if not set.")
 
     # NODES
     allow_nodes:    Optional[list[str]] = Field(default=None,               description="List of nodes to allow. Omit to allow all.")
diff --git a/invokeai/app/services/object_serializer/object_serializer_disk.py b/invokeai/app/services/object_serializer/object_serializer_disk.py
index 7e28320ff2..354a9b0c04 100644
--- a/invokeai/app/services/object_serializer/object_serializer_disk.py
+++ b/invokeai/app/services/object_serializer/object_serializer_disk.py
@@ -1,5 +1,5 @@
-import threading
 import tempfile
+import threading
 import typing
 from dataclasses import dataclass
 from pathlib import Path
@@ -72,7 +72,9 @@ class ObjectSerializerDisk(ObjectSerializerBase[T]):
 
     def _new_name(self) -> str:
         tid = threading.current_thread().ident
-        return f"{self._obj_class_name}_{tid}_{uuid_string()}"
+        # Add tid to the object name because uuid4 not thread-safe on windows
+        # See https://stackoverflow.com/questions/2759644/python-multiprocessing-doesnt-play-nicely-with-uuid-uuid4
+        return f"{self._obj_class_name}_{tid}-{uuid_string()}"
 
     def _tempdir_cleanup(self) -> None:
         """Calls `cleanup` on the temporary directory, if it exists."""
diff --git a/invokeai/app/services/session_processor/session_processor_default.py b/invokeai/app/services/session_processor/session_processor_default.py
index eb00caba5b..1860e4a5b3 100644
--- a/invokeai/app/services/session_processor/session_processor_default.py
+++ b/invokeai/app/services/session_processor/session_processor_default.py
@@ -16,6 +16,7 @@ from invokeai.app.services.session_processor.session_processor_common import Can
 from invokeai.app.services.session_queue.session_queue_common import SessionQueueItem
 from invokeai.app.services.shared.invocation_context import InvocationContextData, build_invocation_context
 from invokeai.app.util.profiler import Profiler
+from invokeai.backend.util.devices import TorchDevice
 
 from ..invoker import Invoker
 from .session_processor_base import SessionProcessorBase
@@ -40,7 +41,9 @@ class DefaultSessionProcessor(SessionProcessorBase):
         self._thread_semaphore = BoundedSemaphore(self._thread_limit)
         self._polling_interval = polling_interval
 
-        self._worker_thread_count = self._invoker.services.configuration.max_threads
+        self._worker_thread_count = self._invoker.services.configuration.max_threads or len(
+            TorchDevice.execution_devices()
+        )
         self._session_worker_queue: Queue[SessionQueueItem] = Queue()
         self._process_lock = Lock()
 
diff --git a/invokeai/backend/util/devices.py b/invokeai/backend/util/devices.py
index b8cdec2ac3..b88206c5f7 100644
--- a/invokeai/backend/util/devices.py
+++ b/invokeai/backend/util/devices.py
@@ -1,4 +1,6 @@
-from typing import TYPE_CHECKING, Dict, Literal, Optional, Union
+"""Torch Device class provides torch device selection services."""
+
+from typing import TYPE_CHECKING, Dict, List, Literal, Optional, Union
 
 import torch
 from deprecated import deprecated
@@ -69,6 +71,14 @@ class TorchDevice:
             device = CPU_DEVICE
         return cls.normalize(device)
 
+    @classmethod
+    def execution_devices(cls) -> List[torch.device]:
+        """Return a list of torch.devices that can be used for accelerated inference."""
+        if cls._model_cache:
+            return cls._model_cache.execution_devices
+        else:
+            return [cls.choose_torch_device]
+
     @classmethod
     def choose_torch_dtype(cls, device: Optional[torch.device] = None) -> torch.dtype:
         """Return the precision to use for accelerated inference."""