diff --git a/pydantic_ai_slim/pydantic_ai/_cli.py b/pydantic_ai_slim/pydantic_ai/_cli.py
index bc3f2a271b..99f4ef1eb8 100644
--- a/pydantic_ai_slim/pydantic_ai/_cli.py
+++ b/pydantic_ai_slim/pydantic_ai/_cli.py
@@ -228,7 +228,7 @@ async def run_chat(
     prog_name: str,
     config_dir: Path | None = None,
     deps: AgentDepsT = None,
-    message_history: list[ModelMessage] | None = None,
+    message_history: Sequence[ModelMessage] | None = None,
 ) -> int:
     prompt_history_path = (config_dir or PYDANTIC_AI_HOME) / PROMPT_HISTORY_FILENAME
     prompt_history_path.parent.mkdir(parents=True, exist_ok=True)
@@ -236,7 +236,7 @@ async def run_chat(
     session: PromptSession[Any] = PromptSession(history=FileHistory(str(prompt_history_path)))
 
     multiline = False
-    messages: list[ModelMessage] = message_history[:] if message_history else []
+    messages: list[ModelMessage] = list(message_history) if message_history else []
 
     while True:
         try:
@@ -272,7 +272,7 @@ async def ask_agent(
     console: Console,
     code_theme: str,
     deps: AgentDepsT = None,
-    messages: list[ModelMessage] | None = None,
+    messages: Sequence[ModelMessage] | None = None,
 ) -> list[ModelMessage]:
     status = Status('[dim]Working on it…[/dim]', console=console)
 
diff --git a/pydantic_ai_slim/pydantic_ai/agent/__init__.py b/pydantic_ai_slim/pydantic_ai/agent/__init__.py
index 72c256e9c4..9ba8420299 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/__init__.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/__init__.py
@@ -415,7 +415,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -432,7 +432,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -449,7 +449,7 @@ async def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -566,7 +566,7 @@ async def main():
         # Build the initial state
         usage = usage or _usage.RunUsage()
         state = _agent_graph.GraphAgentState(
-            message_history=message_history[:] if message_history else [],
+            message_history=list(message_history) if message_history else [],
             usage=usage,
             retries=0,
             run_step=0,
@@ -690,7 +690,7 @@ def _run_span_end_attributes(
             }
         else:
             attrs = {
-                'pydantic_ai.all_messages': json.dumps(settings.messages_to_otel_messages(state.message_history)),
+                'pydantic_ai.all_messages': json.dumps(settings.messages_to_otel_messages(list(state.message_history))),
                 **settings.system_instructions_attributes(literal_instructions),
             }
 
diff --git a/pydantic_ai_slim/pydantic_ai/agent/abstract.py b/pydantic_ai_slim/pydantic_ai/agent/abstract.py
index fdd21b8065..6973b7160c 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/abstract.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/abstract.py
@@ -126,7 +126,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -144,7 +144,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -161,7 +161,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -240,7 +240,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -258,7 +258,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -275,7 +275,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -346,7 +346,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -364,7 +364,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -382,7 +382,7 @@ async def run_stream(  # noqa C901
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -558,7 +558,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -575,7 +575,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -593,7 +593,7 @@ async def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -944,7 +944,7 @@ async def to_cli(
         self: Self,
         deps: AgentDepsT = None,
         prog_name: str = 'pydantic-ai',
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
     ) -> None:
         """Run the agent in a CLI chat interface.
 
@@ -981,7 +981,7 @@ def to_cli_sync(
         self: Self,
         deps: AgentDepsT = None,
         prog_name: str = 'pydantic-ai',
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
     ) -> None:
         """Run the agent in a CLI chat interface with the non-async interface.
 
diff --git a/pydantic_ai_slim/pydantic_ai/agent/wrapper.py b/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
index ba735f0907..4e8646d040 100644
--- a/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
+++ b/pydantic_ai_slim/pydantic_ai/agent/wrapper.py
@@ -72,7 +72,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -89,7 +89,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -106,7 +106,7 @@ async def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
diff --git a/pydantic_ai_slim/pydantic_ai/direct.py b/pydantic_ai_slim/pydantic_ai/direct.py
index 38c92f71eb..034bc11fbf 100644
--- a/pydantic_ai_slim/pydantic_ai/direct.py
+++ b/pydantic_ai_slim/pydantic_ai/direct.py
@@ -10,7 +10,7 @@
 
 import queue
 import threading
-from collections.abc import Iterator
+from collections.abc import Iterator, Sequence
 from contextlib import AbstractAsyncContextManager
 from dataclasses import dataclass, field
 from datetime import datetime
@@ -35,7 +35,7 @@
 
 async def model_request(
     model: models.Model | models.KnownModelName | str,
-    messages: list[messages.ModelMessage],
+    messages: Sequence[messages.ModelMessage],
     *,
     model_settings: settings.ModelSettings | None = None,
     model_request_parameters: models.ModelRequestParameters | None = None,
@@ -79,7 +79,7 @@ async def main():
     """
     model_instance = _prepare_model(model, instrument)
     return await model_instance.request(
-        messages,
+        list(messages),
         model_settings,
         model_request_parameters or models.ModelRequestParameters(),
     )
@@ -87,7 +87,7 @@ async def main():
 
 def model_request_sync(
     model: models.Model | models.KnownModelName | str,
-    messages: list[messages.ModelMessage],
+    messages: Sequence[messages.ModelMessage],
     *,
     model_settings: settings.ModelSettings | None = None,
     model_request_parameters: models.ModelRequestParameters | None = None,
@@ -133,7 +133,7 @@ def model_request_sync(
     return _get_event_loop().run_until_complete(
         model_request(
             model,
-            messages,
+            list(messages),
             model_settings=model_settings,
             model_request_parameters=model_request_parameters,
             instrument=instrument,
@@ -143,7 +143,7 @@ def model_request_sync(
 
 def model_request_stream(
     model: models.Model | models.KnownModelName | str,
-    messages: list[messages.ModelMessage],
+    messages: Sequence[messages.ModelMessage],
     *,
     model_settings: settings.ModelSettings | None = None,
     model_request_parameters: models.ModelRequestParameters | None = None,
@@ -191,7 +191,7 @@ async def main():
     """
     model_instance = _prepare_model(model, instrument)
     return model_instance.request_stream(
-        messages,
+        list(messages),
         model_settings,
         model_request_parameters or models.ModelRequestParameters(),
     )
@@ -199,7 +199,7 @@ async def main():
 
 def model_request_stream_sync(
     model: models.Model | models.KnownModelName | str,
-    messages: list[messages.ModelMessage],
+    messages: Sequence[messages.ModelMessage],
     *,
     model_settings: settings.ModelSettings | None = None,
     model_request_parameters: models.ModelRequestParameters | None = None,
@@ -246,7 +246,7 @@ def model_request_stream_sync(
     """
     async_stream_cm = model_request_stream(
         model=model,
-        messages=messages,
+        messages=list(messages),
         model_settings=model_settings,
         model_request_parameters=model_request_parameters,
         instrument=instrument,
diff --git a/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py b/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
index d7d4987d8f..7590d0b433 100644
--- a/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
+++ b/pydantic_ai_slim/pydantic_ai/durable_exec/dbos/_agent.py
@@ -111,7 +111,7 @@ async def wrapped_run_workflow(
             user_prompt: str | Sequence[_messages.UserContent] | None = None,
             *,
             output_type: OutputSpec[RunOutputDataT] | None = None,
-            message_history: list[_messages.ModelMessage] | None = None,
+            message_history: Sequence[_messages.ModelMessage] | None = None,
             deferred_tool_results: DeferredToolResults | None = None,
             model: models.Model | models.KnownModelName | str | None = None,
             deps: AgentDepsT,
@@ -148,7 +148,7 @@ def wrapped_run_sync_workflow(
             user_prompt: str | Sequence[_messages.UserContent] | None = None,
             *,
             output_type: OutputSpec[RunOutputDataT] | None = None,
-            message_history: list[_messages.ModelMessage] | None = None,
+            message_history: Sequence[_messages.ModelMessage] | None = None,
             deferred_tool_results: DeferredToolResults | None = None,
             model: models.Model | models.KnownModelName | str | None = None,
             deps: AgentDepsT,
@@ -236,7 +236,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -254,7 +254,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -271,7 +271,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -340,7 +340,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -358,7 +358,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -375,7 +375,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -443,7 +443,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -461,7 +461,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -479,7 +479,7 @@ async def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -553,7 +553,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -571,7 +571,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -589,7 +589,7 @@ async def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
diff --git a/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py b/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
index a87b5195a9..bf926c7628 100644
--- a/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
+++ b/pydantic_ai_slim/pydantic_ai/durable_exec/temporal/_agent.py
@@ -258,7 +258,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -276,7 +276,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -293,7 +293,7 @@ async def run(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -368,7 +368,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -386,7 +386,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -403,7 +403,7 @@ def run_sync(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -476,7 +476,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -494,7 +494,7 @@ def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -512,7 +512,7 @@ async def run_stream(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -586,7 +586,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -604,7 +604,7 @@ def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT],
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -622,7 +622,7 @@ async def iter(
         user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         output_type: OutputSpec[RunOutputDataT] | None = None,
-        message_history: list[_messages.ModelMessage] | None = None,
+        message_history: Sequence[_messages.ModelMessage] | None = None,
         deferred_tool_results: DeferredToolResults | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,