diff --git a/libs/langgraph/langgraph/pregel/messages.py b/libs/langgraph/langgraph/pregel/messages.py
index ffb07eddb..867012fa6 100644
--- a/libs/langgraph/langgraph/pregel/messages.py
+++ b/libs/langgraph/langgraph/pregel/messages.py
@@ -127,6 +127,16 @@ class StreamMessagesHandler(BaseCallbackHandler, _StreamingCallbackHandler):
                 tuple(cast(str, metadata["langgraph_checkpoint_ns"]).split(NS_SEP)),
                 metadata,
             )
+            if isinstance(inputs, dict):
+                for key, value in inputs.items():
+                    if isinstance(value, BaseMessage):
+                        if value.id is not None:
+                            self.seen.add(value.id)
+                    elif isinstance(value, Sequence) and not isinstance(value, str):
+                        for item in value:
+                            if isinstance(item, BaseMessage):
+                                if item.id is not None:
+                                    self.seen.add(item.id)
 
     def on_chain_end(
         self,
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index bb5c7d972..e85de648c 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -6588,3 +6588,101 @@ def test_get_stream_writer() -> None:
             },
         ),
     ]
+
+
+def test_stream_messages_dedupe_inputs() -> None:
+    from langchain_core.messages import AIMessage
+
+    def call_model(state):
+        return {"messages": AIMessage("hi", id="1")}
+
+    def route(state):
+        return Command(goto="node_2", graph=Command.PARENT)
+
+    subgraph = (
+        StateGraph(MessagesState)
+        .add_node(call_model)
+        .add_node(route)
+        .add_edge(START, "call_model")
+        .add_edge("call_model", "route")
+        .compile()
+    )
+
+    graph = (
+        StateGraph(MessagesState)
+        .add_node("node_1", subgraph)
+        .add_node("node_2", lambda state: state)
+        .add_edge(START, "node_1")
+        .compile()
+    )
+
+    chunks = [
+        chunk
+        for ns, chunk in graph.stream(
+            {"messages": "hi"}, stream_mode="messages", subgraphs=True
+        )
+    ]
+
+    assert len(chunks) == 1
+    assert chunks[0][0] == AIMessage("hi", id="1")
+    assert chunks[0][1]["langgraph_node"] == "call_model"
+
+
+@pytest.mark.parametrize("checkpointer_name", ALL_CHECKPOINTERS_SYNC)
+def test_stream_messages_dedupe_state(
+    request: pytest.FixtureRequest, checkpointer_name: str
+) -> None:
+    from langchain_core.messages import AIMessage
+
+    checkpointer = request.getfixturevalue(f"checkpointer_{checkpointer_name}")
+    to_emit = [AIMessage("bye", id="1"), AIMessage("bye again", id="2")]
+
+    def call_model(state):
+        return {"messages": to_emit.pop(0)}
+
+    def route(state):
+        return Command(goto="node_2", graph=Command.PARENT)
+
+    subgraph = (
+        StateGraph(MessagesState)
+        .add_node(call_model)
+        .add_node(route)
+        .add_edge(START, "call_model")
+        .add_edge("call_model", "route")
+        .compile()
+    )
+
+    graph = (
+        StateGraph(MessagesState)
+        .add_node("node_1", subgraph)
+        .add_node("node_2", lambda state: state)
+        .add_edge(START, "node_1")
+        .compile(checkpointer=checkpointer)
+    )
+
+    thread1 = {"configurable": {"thread_id": "1"}}
+
+    chunks = [
+        chunk
+        for ns, chunk in graph.stream(
+            {"messages": "hi"}, thread1, stream_mode="messages", subgraphs=True
+        )
+    ]
+
+    assert len(chunks) == 1
+    assert chunks[0][0] == AIMessage("bye", id="1")
+    assert chunks[0][1]["langgraph_node"] == "call_model"
+
+    chunks = [
+        chunk
+        for ns, chunk in graph.stream(
+            {"messages": "hi again"},
+            thread1,
+            stream_mode="messages",
+            subgraphs=True,
+        )
+    ]
+
+    assert len(chunks) == 1
+    assert chunks[0][0] == AIMessage("bye again", id="2")
+    assert chunks[0][1]["langgraph_node"] == "call_model"
diff --git a/libs/langgraph/tests/test_pregel_async.py b/libs/langgraph/tests/test_pregel_async.py
index f369a7aa7..5db138c8f 100644
--- a/libs/langgraph/tests/test_pregel_async.py
+++ b/libs/langgraph/tests/test_pregel_async.py
@@ -7282,9 +7282,7 @@ async def test_multiple_subgraphs_mixed_state_graph(
 
 @NEEDS_CONTEXTVARS
 @pytest.mark.parametrize("checkpointer_name", ALL_CHECKPOINTERS_ASYNC)
-async def test_multiple_subgraphs_checkpointer(
-    request: pytest.FixtureRequest, checkpointer_name: str
-) -> None:
+async def test_multiple_subgraphs_checkpointer(checkpointer_name: str) -> None:
     async with awith_checkpointer(checkpointer_name) as checkpointer:
 
         class SubgraphState(TypedDict):
@@ -7513,3 +7511,99 @@ async def test_tags_stream_mode_messages() -> None:
             },
         )
     ]
+
+
+async def test_stream_messages_dedupe_inputs() -> None:
+    from langchain_core.messages import AIMessage
+
+    async def call_model(state):
+        return {"messages": AIMessage("hi", id="1")}
+
+    async def route(state):
+        return Command(goto="node_2", graph=Command.PARENT)
+
+    subgraph = (
+        StateGraph(MessagesState)
+        .add_node(call_model)
+        .add_node(route)
+        .add_edge(START, "call_model")
+        .add_edge("call_model", "route")
+        .compile()
+    )
+
+    graph = (
+        StateGraph(MessagesState)
+        .add_node("node_1", subgraph)
+        .add_node("node_2", lambda state: state)
+        .add_edge(START, "node_1")
+        .compile()
+    )
+
+    chunks = [
+        chunk
+        async for ns, chunk in graph.astream(
+            {"messages": "hi"}, stream_mode="messages", subgraphs=True
+        )
+    ]
+
+    assert len(chunks) == 1
+    assert chunks[0][0] == AIMessage("hi", id="1")
+    assert chunks[0][1]["langgraph_node"] == "call_model"
+
+
+@pytest.mark.parametrize("checkpointer_name", ALL_CHECKPOINTERS_ASYNC)
+async def test_stream_messages_dedupe_state(checkpointer_name: str) -> None:
+    async with awith_checkpointer(checkpointer_name) as checkpointer:
+        from langchain_core.messages import AIMessage
+
+        to_emit = [AIMessage("bye", id="1"), AIMessage("bye again", id="2")]
+
+        async def call_model(state):
+            return {"messages": to_emit.pop(0)}
+
+        async def route(state):
+            return Command(goto="node_2", graph=Command.PARENT)
+
+        subgraph = (
+            StateGraph(MessagesState)
+            .add_node(call_model)
+            .add_node(route)
+            .add_edge(START, "call_model")
+            .add_edge("call_model", "route")
+            .compile()
+        )
+
+        graph = (
+            StateGraph(MessagesState)
+            .add_node("node_1", subgraph)
+            .add_node("node_2", lambda state: state)
+            .add_edge(START, "node_1")
+            .compile(checkpointer=checkpointer)
+        )
+
+        thread1 = {"configurable": {"thread_id": "1"}}
+
+        chunks = [
+            chunk
+            async for ns, chunk in graph.astream(
+                {"messages": "hi"}, thread1, stream_mode="messages", subgraphs=True
+            )
+        ]
+
+        assert len(chunks) == 1
+        assert chunks[0][0] == AIMessage("bye", id="1")
+        assert chunks[0][1]["langgraph_node"] == "call_model"
+
+        chunks = [
+            chunk
+            async for ns, chunk in graph.astream(
+                {"messages": "hi again"},
+                thread1,
+                stream_mode="messages",
+                subgraphs=True,
+            )
+        ]
+
+        assert len(chunks) == 1
+        assert chunks[0][0] == AIMessage("bye again", id="2")
+        assert chunks[0][1]["langgraph_node"] == "call_model"