diff --git a/substrate/core/corenode.py b/substrate/core/corenode.py
index 79edffe..638da64 100644
--- a/substrate/core/corenode.py
+++ b/substrate/core/corenode.py
@@ -24,7 +24,7 @@ def __init__(
         _cache_age: Optional[int] = None,
         _cache_keys: Optional[List[str]] = None,
         _max_retries: Optional[int] = None,
-        _depends: List["CoreNode"] = [],
+        _depends: Optional[List["CoreNode"]] = None,
         **attr,
     ):
         self._out_type = out_type
@@ -35,7 +35,7 @@ def __init__(
         self._cache_age = _cache_age
         self._cache_keys = _cache_keys
         self._max_retries = _max_retries
-        self._depends = _depends
+        self._depends = [] if _depends is None else _depends
         self._should_output_globally: bool = not hide
         self.SG = nx.DiGraph()
         if attr:
@@ -54,6 +54,10 @@ def __init__(
             for referenced_future in depend_node.futures_from_args:
                 self.futures_from_args.append(referenced_future)
 
+    @property
+    def explicit_depends(self) -> List["CoreNode"]:
+        return self._depends
+
     @property
     def dependent_futures(self) -> List[Future]:
         return find_futures_client(self.init_attrs)
diff --git a/substrate/core/future_directive.py b/substrate/core/future_directive.py
index 349af21..5a9dc27 100644
--- a/substrate/core/future_directive.py
+++ b/substrate/core/future_directive.py
@@ -89,7 +89,7 @@ class TraceOperation:
 @dataclass
 class TraceDirective(BaseDirective):
     op_stack: List[TraceOperation]
-    origin_node: Any  # Should be CoreNode, but am running into circular import
+    origin_node: "CoreNode"
     type: Literal["trace"] = "trace"
 
     def to_dict(self) -> Dict:
diff --git a/substrate/run_python.py b/substrate/run_python.py
index 5ef588b..f8eaca7 100644
--- a/substrate/run_python.py
+++ b/substrate/run_python.py
@@ -11,13 +11,13 @@ class RunPython(CoreNode[RunPythonOut]):
     def __init__(
         self,
         function: Callable,
-        kwargs: Dict[str, Any] = {},
+        kwargs=None,
         pip_install: Optional[List[str]] = None,
         hide: bool = False,
         _cache_age: Optional[int] = None,
         _cache_keys: Optional[List[str]] = None,
         _max_retries: Optional[int] = None,
-        _depends: List[CoreNode] = [],
+        _depends: Optional[List[CoreNode]] = None,
     ):
         """
         Args:
@@ -41,7 +41,7 @@ def __init__(
         python_version = sys.version.split()[0]
         super().__init__(
             pkl_function=fn_str,
-            kwargs=kwargs,
+            kwargs={} if kwargs is None else kwargs,
             pip_install=pip_install,
             hide=hide,
             python_version=python_version,
diff --git a/substrate/substrate.py b/substrate/substrate.py
index f0f1fb8..1fa19d8 100644
--- a/substrate/substrate.py
+++ b/substrate/substrate.py
@@ -1,7 +1,8 @@
 import json
+from typing import Optional, Any, Dict
+
 import zlib
 import base64
-from typing import Any, Dict
 
 from substrate.streaming import SubstrateStreamingResponse
 
@@ -21,11 +22,13 @@ def __init__(
         api_key: str,
         base_url: str = "https://api.substrate.run",
         timeout: float = 60 * 5.0,
-        additional_headers: Dict[str, Any] = {},
+        additional_headers: Optional[Dict[str, Any]] = None,
     ):
         """
         Initialize the Substrate SDK.
         """
+        if additional_headers is None:
+            additional_headers = {}
         self.api_key = api_key
         self._client = APIClient(
             api_key=api_key,
@@ -98,7 +101,7 @@ def collect_nodes(node):
         for node in all_nodes:
             if not graph.DAG.has_node(node):
                 graph.add_node(node)
-            for depend_node in node._depends:
+            for depend_node in node.explicit_depends:
                 graph.add_edge(depend_node, node)
         graph_serialized = graph.to_dict()
         return graph_serialized