diff --git a/src/controlflow/core/agent/agent.py b/src/controlflow/core/agent/agent.py
index e8e40002..ac81f43f 100644
--- a/src/controlflow/core/agent/agent.py
+++ b/src/controlflow/core/agent/agent.py
@@ -5,6 +5,7 @@
 from contextlib import contextmanager
 from typing import TYPE_CHECKING, Any, Callable, Optional
 
+from langchain_core.language_models import BaseChatModel
 from pydantic import Field, field_serializer
 
 import controlflow
@@ -60,11 +61,11 @@ class Agent(ControlFlowModel):
         description="The memory object used by the agent. If not specified, an in-memory memory object will be used. Pass None to disable memory.",
     )
 
-    # note: `model` should be typed as a BaseChatModel but V2 models can't have
+    # note: `model` should be typed as Optional[BaseChatModel] but V2 models can't have
     # V1 attributes without erroring, so we have to use Any.
-    model: Any = Field(
+    model: Optional[Any] = Field(
+        None,
         description="The LangChain BaseChatModel used by the agent. If not provided, the default model will be used.",
-        default_factory=get_default_model,
         exclude=True,
     )
 
@@ -85,6 +86,9 @@ def __init__(self, name=None, **kwargs):
             kwargs["name"] = name
         super().__init__(**kwargs)
 
+    def get_model(self) -> BaseChatModel:
+        return self.model or get_default_model()
+
     def get_tools(self) -> list[Callable]:
         tools = self.tools.copy()
         if self.user_access:
diff --git a/src/controlflow/core/controller/controller.py b/src/controlflow/core/controller/controller.py
index 39659a08..70d42ac3 100644
--- a/src/controlflow/core/controller/controller.py
+++ b/src/controlflow/core/controller/controller.py
@@ -228,7 +228,7 @@ async def run_once_async(self) -> list[MessageType]:
             with ctx(agent=agent, flow=self.flow, controller=self):
                 response_gen = await completion_async(
                     messages=payload["messages"],
-                    model=agent.model,
+                    model=agent.get_model(),
                     tools=payload["tools"],
                     handlers=payload["handlers"],
                     max_iterations=1,
@@ -264,7 +264,7 @@ def run_once(self) -> list[MessageType]:
         with ctx(agent=agent, flow=self.flow, controller=self):
             response_gen = completion(
                 messages=payload["messages"],
-                model=agent.model,
+                model=agent.get_model(),
                 tools=payload["tools"],
                 handlers=payload["handlers"],
                 max_iterations=1,
diff --git a/tests/core/test_agents.py b/tests/core/test_agents.py
index 00760bd4..bddb6783 100644
--- a/tests/core/test_agents.py
+++ b/tests/core/test_agents.py
@@ -2,6 +2,7 @@
 from controlflow.core.agent import Agent, get_default_agent
 from controlflow.core.agent.names import NAMES
 from controlflow.core.task import Task
+from langchain_openai import ChatOpenAI
 
 
 class TestAgentInitialization:
@@ -13,17 +14,30 @@ def test_agent_gets_random_name(self):
     def test_agent_default_model(self):
         agent = Agent()
 
-        assert agent.model is controlflow.get_default_model()
+        # None indicates it will be loaded from the default model
+        assert agent.model is None
+        assert agent.get_model() is controlflow.get_default_model()
+
+    def test_agent_model(self):
+        model = ChatOpenAI(model="gpt-3.5-turbo")
+        agent = Agent(model=model)
+
+        # None indicates it will be loaded from the default model
+        assert agent.model is model
+        assert agent.get_model() is model
 
 
 class TestDefaultAgent:
-    def test_default_agent_is_marvin(self):
-        agent = get_default_agent()
-        assert agent.name == "Marvin"
+    def test_default_agent(self):
+        assert get_default_agent().name == "Marvin"
+        assert Task("task").get_agents()[0] is get_default_agent()
 
     def test_default_agent_has_no_tools(self):
         assert get_default_agent().tools == []
 
+    def test_default_agent_has_no_model(self):
+        assert get_default_agent().model is None
+
     def test_default_agent_can_be_assigned(self):
         # baseline
         assert get_default_agent().name == "Marvin"
@@ -35,6 +49,14 @@ def test_default_agent_can_be_assigned(self):
         assert Task("task").get_agents()[0] is new_default_agent
         assert [a.name for a in Task("task").get_agents()] == ["New Agent"]
 
-    def test_default_agent(self):
-        assert get_default_agent().name == "Marvin"
-        assert Task("task").get_agents()[0] is get_default_agent()
+    def test_updating_the_default_model_updates_the_default_agent_model(self):
+        new_model = ChatOpenAI(model="gpt-3.5-turbo")
+        controlflow.default_model = new_model
+
+        new_agent = get_default_agent()
+        assert new_agent.model is None
+        assert new_agent.get_model() is new_model
+
+        task = Task("task")
+        assert task.get_agents()[0].model is None
+        assert task.get_agents()[0].get_model() is new_model