diff --git a/libs/checkpoint-postgres/tests/test_async.py b/libs/checkpoint-postgres/tests/test_async.py
index e342548a7..14d4508da 100644
--- a/libs/checkpoint-postgres/tests/test_async.py
+++ b/libs/checkpoint-postgres/tests/test_async.py
@@ -377,13 +377,13 @@ async def test_get_checkpoint_no_channel_values(
 async def test_delta_channel_chain_reconstruction(saver_name: str) -> None:
     """AsyncPostgresSaver reconstructs DeltaChannel chain via point-lookup traversal."""
     pytest.importorskip(
-        "langgraph.channels.delta", reason="langgraph core not installed"
+        "langgraph.channels._delta", reason="langgraph core not installed"
     )
 
     from typing import Annotated
 
     from langchain_core.messages import AIMessage, HumanMessage
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
     from typing_extensions import TypedDict
diff --git a/libs/langgraph/langgraph/channels/__init__.py b/libs/langgraph/langgraph/channels/__init__.py
index cc7fcc471..a69c230b5 100644
--- a/libs/langgraph/langgraph/channels/__init__.py
+++ b/libs/langgraph/langgraph/channels/__init__.py
@@ -1,7 +1,6 @@
 from langgraph.channels.any_value import AnyValue
 from langgraph.channels.base import BaseChannel
 from langgraph.channels.binop import BinaryOperatorAggregate
-from langgraph.channels.delta import DeltaChannel
 from langgraph.channels.ephemeral_value import EphemeralValue
 from langgraph.channels.last_value import LastValue, LastValueAfterFinish
 from langgraph.channels.named_barrier_value import (
@@ -21,7 +20,6 @@ __all__ = (
     "UntrackedValue",
     "EphemeralValue",
     "BinaryOperatorAggregate",
-    "DeltaChannel",
     "NamedBarrierValue",
     "NamedBarrierValueAfterFinish",
     # topics
diff --git a/libs/langgraph/langgraph/channels/delta.py b/libs/langgraph/langgraph/channels/_delta.py
similarity index 93%
rename from libs/langgraph/langgraph/channels/delta.py
rename to libs/langgraph/langgraph/channels/_delta.py
index e8dd955c2..3239d237b 100644
--- a/libs/langgraph/langgraph/channels/delta.py
+++ b/libs/langgraph/langgraph/channels/_delta.py
@@ -23,7 +23,13 @@ def _empty(typ: Any) -> Any:
 
 
 class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
-    """A channel that stores only a sentinel in checkpoints; per-step writes are
+    """Experimental — private API, subject to change or removal without notice.
+
+    Imported from the underscored module `langgraph.channels._delta` on purpose;
+    not re-exported from `langgraph.channels`. Intended for internal use only
+    while we validate the design on real workloads.
+
+    A channel that stores only a sentinel in checkpoints; per-step writes are
     stored in checkpoint_writes and replayed through the operator at load time.
 
     Use with append-style reducers (e.g. `add_messages`) on long-running threads
@@ -36,6 +42,8 @@ class DeltaChannel(Generic[Value], BaseChannel[Any, Any, Any]):
 
     Usage::
 
+        from langgraph.channels._delta import DeltaChannel
+
         class State(TypedDict):
             messages: Annotated[list[AnyMessage], DeltaChannel(add_messages)]
     """
diff --git a/libs/langgraph/langgraph/graph/state.py b/libs/langgraph/langgraph/graph/state.py
index 78cdbb10a..a66062717 100644
--- a/libs/langgraph/langgraph/graph/state.py
+++ b/libs/langgraph/langgraph/graph/state.py
@@ -49,7 +49,7 @@ from langgraph._internal._runnable import coerce_to_runnable
 from langgraph._internal._typing import EMPTY_SEQ, MISSING, DeprecatedKwargs
 from langgraph.channels.base import BaseChannel
 from langgraph.channels.binop import BinaryOperatorAggregate, _strip_extras
-from langgraph.channels.delta import DeltaChannel
+from langgraph.channels._delta import DeltaChannel
 from langgraph.channels.ephemeral_value import EphemeralValue
 from langgraph.channels.last_value import LastValue, LastValueAfterFinish
 from langgraph.channels.named_barrier_value import (
diff --git a/libs/langgraph/langgraph/pregel/_checkpoint.py b/libs/langgraph/langgraph/pregel/_checkpoint.py
index f3c7f1102..3437692be 100644
--- a/libs/langgraph/langgraph/pregel/_checkpoint.py
+++ b/libs/langgraph/langgraph/pregel/_checkpoint.py
@@ -9,7 +9,7 @@ from langgraph.checkpoint.base.id import uuid6
 
 from langgraph._internal._typing import MISSING
 from langgraph.channels.base import BaseChannel
-from langgraph.channels.delta import DeltaChannel
+from langgraph.channels._delta import DeltaChannel
 from langgraph.managed.base import ManagedValueMapping, ManagedValueSpec
 
 LATEST_VERSION = 4
diff --git a/libs/langgraph/tests/test_channels.py b/libs/langgraph/tests/test_channels.py
index 4fd3bb9d3..2b858b6a0 100644
--- a/libs/langgraph/tests/test_channels.py
+++ b/libs/langgraph/tests/test_channels.py
@@ -7,7 +7,7 @@ from langgraph.checkpoint.base import DELTA_SENTINEL
 
 from langgraph._internal._typing import MISSING
 from langgraph.channels.binop import BinaryOperatorAggregate
-from langgraph.channels.delta import DeltaChannel
+from langgraph.channels._delta import DeltaChannel
 from langgraph.channels.last_value import LastValue
 from langgraph.channels.topic import Topic
 from langgraph.channels.untracked_value import UntrackedValue
@@ -127,7 +127,7 @@ def test_delta_channel_basic_two_steps() -> None:
     from langchain_core.messages import AIMessage, HumanMessage
     from langgraph.checkpoint.base import DELTA_SENTINEL
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     ch = DeltaChannel(add_messages).from_checkpoint(MISSING)
@@ -152,7 +152,7 @@ def test_delta_channel_from_checkpoint_writes_list() -> None:
     """replay_writes on a fresh channel replays through the operator."""
     from langchain_core.messages import AIMessage, HumanMessage
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     spec = DeltaChannel(add_messages)
@@ -174,7 +174,7 @@ def test_delta_channel_from_checkpoint_writes_list() -> None:
 def test_delta_channel_from_checkpoint_backwards_compat() -> None:
     from langchain_core.messages import HumanMessage
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     # Old BinaryOperatorAggregate checkpoint: plain list treated as backward compat
@@ -188,7 +188,7 @@ def test_delta_channel_overwrite() -> None:
     from langchain_core.messages import HumanMessage
     from langgraph.checkpoint.base import DELTA_SENTINEL
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
     from langgraph.types import Overwrite
 
@@ -207,7 +207,7 @@ def test_delta_channel_remove_message_and_replay() -> None:
     """RemoveMessage must round-trip correctly when writes are replayed."""
     from langchain_core.messages import AIMessage, HumanMessage, RemoveMessage
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     spec = DeltaChannel(add_messages)
@@ -241,7 +241,7 @@ def test_delta_channel_update_by_id_and_replay() -> None:
     """Updating a message by ID must round-trip correctly through writes replay."""
     from langchain_core.messages import HumanMessage
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     spec = DeltaChannel(add_messages)
@@ -270,7 +270,7 @@ def test_delta_channel_checkpoint_returns_sentinel() -> None:
     """checkpoint() always returns DELTA_SENTINEL regardless of state."""
     from langgraph.checkpoint.base import DELTA_SENTINEL
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.message import add_messages
 
     ch = DeltaChannel(add_messages).from_checkpoint(MISSING)
@@ -290,7 +290,7 @@ def test_delta_channel_inmemory_saver_assembles_writes() -> None:
     from langgraph.checkpoint.memory import InMemorySaver
     from typing_extensions import TypedDict
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
 
@@ -329,7 +329,7 @@ def _delta_channel_with_type(operator, typ):
     """Build a DeltaChannel with an explicit type via the Annotated injection path."""
     from typing import Annotated
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.state import _get_channel
 
     return _get_channel("_test", Annotated[typ, DeltaChannel(operator)])
@@ -464,7 +464,7 @@ def test_delta_channel_dict_reducer_with_notrequired_annotation() -> None:
 
     from typing_extensions import NotRequired
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph.state import _get_channel
 
     def merge_dicts(left: dict | None, right: dict) -> dict:
@@ -494,7 +494,7 @@ def test_delta_channel_dict_reducer_end_to_end_filesystem() -> None:
     from langgraph.checkpoint.memory import InMemorySaver
     from typing_extensions import TypedDict
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
 
     def merge_files(left: dict | None, right: dict) -> dict:
diff --git a/libs/langgraph/tests/test_delta_channel_benchmark.py b/libs/langgraph/tests/test_delta_channel_benchmark.py
index ab710ebcd..bc393d804 100644
--- a/libs/langgraph/tests/test_delta_channel_benchmark.py
+++ b/libs/langgraph/tests/test_delta_channel_benchmark.py
@@ -26,7 +26,7 @@ from langchain_core.messages import AIMessage, HumanMessage
 from langgraph.checkpoint.memory import MemorySaver
 from typing_extensions import TypedDict
 
-from langgraph.channels.delta import DeltaChannel
+from langgraph.channels._delta import DeltaChannel
 from langgraph.graph import END, StateGraph
 from langgraph.graph.message import add_messages
 
diff --git a/libs/langgraph/tests/test_delta_channel_migration.py b/libs/langgraph/tests/test_delta_channel_migration.py
index 72286522f..bdaa1e6ea 100644
--- a/libs/langgraph/tests/test_delta_channel_migration.py
+++ b/libs/langgraph/tests/test_delta_channel_migration.py
@@ -50,7 +50,7 @@ from langgraph.checkpoint.memory import InMemorySaver
 from typing_extensions import TypedDict
 
 from langgraph.channels.binop import BinaryOperatorAggregate
-from langgraph.channels.delta import DeltaChannel
+from langgraph.channels._delta import DeltaChannel
 from langgraph.graph import END, START, StateGraph
 
 pytestmark = pytest.mark.anyio
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index 9ca522bd8..474e08c51 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -9407,7 +9407,7 @@ async def test_delta_channel_end_to_end_inmemory() -> None:
     from langchain_core.messages import AIMessage, HumanMessage
     from langgraph.checkpoint.memory import InMemorySaver
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
 
@@ -9449,7 +9449,7 @@ async def test_delta_channel_time_travel() -> None:
     from langchain_core.messages import AIMessage, HumanMessage
     from langgraph.checkpoint.memory import InMemorySaver
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
 
@@ -9507,7 +9507,7 @@ async def test_delta_channel_remove_message_end_to_end() -> None:
     from langchain_core.messages import AIMessage, HumanMessage, RemoveMessage
     from langgraph.checkpoint.memory import InMemorySaver
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages
 
@@ -9554,7 +9554,7 @@ async def test_delta_channel_update_by_id_end_to_end() -> None:
     from langchain_core.messages import HumanMessage
     from langgraph.checkpoint.memory import InMemorySaver
 
-    from langgraph.channels.delta import DeltaChannel
+    from langgraph.channels._delta import DeltaChannel
     from langgraph.graph import START, StateGraph
     from langgraph.graph.message import add_messages