diff --git a/sdks/python/apache_beam/runners/worker/data_plane.py b/sdks/python/apache_beam/runners/worker/data_plane.py
index cbd28f8b0a3f..e46e66bd11d3 100644
--- a/sdks/python/apache_beam/runners/worker/data_plane.py
+++ b/sdks/python/apache_beam/runners/worker/data_plane.py
@@ -49,6 +49,7 @@
 from apache_beam.portability.api import beam_fn_api_pb2_grpc
 from apache_beam.runners.worker.channel_factory import GRPCChannelFactory
 from apache_beam.runners.worker.worker_id_interceptor import WorkerIdInterceptor
+from apache_beam.utils.byte_limited_queue import ByteLimitedQueue
 
 if TYPE_CHECKING:
   import apache_beam.coders.slow_stream
@@ -455,10 +456,20 @@ class _GrpcDataChannel(DataChannel):
 
   def __init__(self, data_buffer_time_limit_ms=0):
     # type: (int) -> None
+    def _element_weight(element):
+      if isinstance(element, beam_fn_api_pb2.Elements.Data):
+        return len(element.data)
+      elif isinstance(element, beam_fn_api_pb2.Elements.Timers):
+        return len(element.timers)
+      return 0
+
     self._data_buffer_time_limit_ms = data_buffer_time_limit_ms
-    self._to_send = queue.Queue()  # type: queue.Queue[DataOrTimers]
+    self._to_send = ByteLimitedQueue(
+        maxsize=10000, maxweight=100 << 20,
+        weighing_fn=_element_weight)  # type: queue.Queue[DataOrTimers]
     self._received = collections.defaultdict(
-        lambda: queue.Queue(maxsize=5)
+        lambda: ByteLimitedQueue(
+            maxsize=5, maxweight=100 << 20, weighing_fn=_element_weight)
     )  # type: DefaultDict[str, queue.Queue[DataOrTimers]]
 
     # Keep a cache of completed instructions. Data for completed instructions
diff --git a/sdks/python/apache_beam/utils/byte_limited_queue.py b/sdks/python/apache_beam/utils/byte_limited_queue.py
new file mode 100644
index 000000000000..9bb4d469ae2a
--- /dev/null
+++ b/sdks/python/apache_beam/utils/byte_limited_queue.py
@@ -0,0 +1,96 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""A thread-safe queue that limits capacity by total byte size."""
+
+import queue
+import time
+from typing import Any
+from typing import Callable
+
+
+class ByteLimitedQueue(queue.Queue):
+  """A queue.Queue that limits by both element count and total weight.
+
+  A single element is allowed to exceed the maxweight to avoid deadlock.
+  Note that shutdown is only supported after there are no more put calls.
+  """
+  def __init__(
+      self,
+      weighing_fn,  # type: Callable[[Any], int]
+      maxsize=0,  # type: int
+      maxweight=0,  # type: int
+  ):
+    # type: (...) -> None
+
+    """Initializes a ByteLimitedQueue.
+
+    Args:
+      weighing_fn: A Callable that accepts an item and returns its integer
+        weight.
+      maxsize: The maximum number of items allowed in the queue. If 0 or
+        negative, there is no limit on the number of elements.
+      maxweight: The maximum accumulated weight allowed in the queue.
+    """
+    super().__init__(maxsize=0)
+    self.max_elements = maxsize
+    self.max_weight = maxweight
+    self.weighing_fn = weighing_fn
+    self._byte_size = 0
+
+  def _is_full(self, item_size):
+    if self._qsize() == 0:
+      return False
+    if self.max_elements > 0 and self._qsize() >= self.max_elements:
+      return True
+    if self.max_weight > 0 and self._byte_size + item_size > self.max_weight:
+      return True
+    return False
+
+  def put(self, item, block=True, timeout=None):
+    item_size = max(1, self.weighing_fn(item))
+    with self.not_full:
+      if not block:
+        if self._is_full(item_size):
+          raise queue.Full
+      elif timeout is None:
+        while self._is_full(item_size):
+          self.not_full.wait()
+      elif timeout < 0:
+        raise ValueError("'timeout' must be a non-negative number")
+      else:
+        endtime = time.monotonic() + timeout
+        while self._is_full(item_size):
+          remaining = endtime - time.monotonic()
+          if remaining <= 0.0:
+            raise queue.Full
+          self.not_full.wait(remaining)
+
+      self._put((item, item_size))
+      self._byte_size += item_size
+      self.unfinished_tasks += 1
+      self.not_empty.notify()
+
+  def _get(self):
+    item, item_weight = super()._get()
+    self._byte_size -= item_weight
+    return item
+
+  def byte_size(self):
+    """Return the total byte weight of elements in the queue."""
+    with self.mutex:
+      return self._byte_size
diff --git a/sdks/python/apache_beam/utils/byte_limited_queue_test.py b/sdks/python/apache_beam/utils/byte_limited_queue_test.py
new file mode 100644
index 000000000000..e6349f3af00b
--- /dev/null
+++ b/sdks/python/apache_beam/utils/byte_limited_queue_test.py
@@ -0,0 +1,168 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Unit tests for byte-limited queue."""
+
+import queue
+import sys
+import threading
+import time
+import unittest
+
+from apache_beam.utils.byte_limited_queue import ByteLimitedQueue
+
+
+class FakeItem(object):
+  def __init__(self, size):
+    self._size = size
+
+  def weight(self):
+    return self._size
+
+
+class ByteLimitedQueueTest(unittest.TestCase):
+  def test_unbounded(self):
+    bq = ByteLimitedQueue(lambda x: x.weight())
+    for i in range(200):
+      bq.put(FakeItem(i))
+    # Add 1 since weight of zero is set to 1
+    self.assertEqual(bq.byte_size(), sum(range(200)) + 1)
+    self.assertEqual(bq.qsize(), 200)
+
+  def test_put_and_get(self):
+    bq = ByteLimitedQueue(lambda x: x.weight(), maxweight=200)
+    bq.put(FakeItem(50))
+    bq.put(FakeItem(140))
+    self.assertEqual(bq.byte_size(), 190)
+    self.assertEqual(bq.qsize(), 2)
+    # Putting another would exceed 200.
+    with self.assertRaises(queue.Full):
+      bq.put(FakeItem(20), block=False)
+    bq.put(FakeItem(10), block=False)
+    self.assertEqual(bq.byte_size(), 200)
+    self.assertEqual(bq.qsize(), 3)
+
+    self.assertEqual(bq.get().weight(), 50)
+    self.assertEqual(bq.byte_size(), 150)
+    self.assertEqual(bq.qsize(), 2)
+    bq.put(FakeItem(20), block=False)
+
+  def test_dual_limit(self):
+    # Queue limits: at most 2 items, OR at most 100 weight.
+    bq = ByteLimitedQueue(lambda x: x.weight(), maxsize=3, maxweight=100)
+    bq.put(FakeItem(30))
+    bq.put(FakeItem(40))
+    bq.put(FakeItem(20))
+    self.assertEqual(bq.byte_size(), 90)
+    self.assertEqual(bq.qsize(), 3)
+    # Full on element count (size=2).
+    with self.assertRaises(queue.Full):
+      bq.put(FakeItem(10), block=False)
+    self.assertEqual(bq.get().weight(), 30)
+    self.assertEqual(bq.get().weight(), 40)
+    bq.put(FakeItem(10))
+    # Full on byte count
+    with self.assertRaises(queue.Full):
+      bq.put(FakeItem(90), block=False)
+    self.assertEqual(bq.get().weight(), 20)
+    bq.put(FakeItem(90), block=False)
+
+  @unittest.skipIf(sys.version_info < (3, 13), 'Queue.ShutDown added in 3.13.')
+  def test_multithreading(self):
+    bq = ByteLimitedQueue(lambda x: x.weight(), maxsize=0, maxweight=100)
+    received = []
+
+    def producer():
+      for i in range(101):
+        bq.put(FakeItem(i))
+
+    def consumer():
+      while True:
+        try:
+          received.append(bq.get().weight())
+        except queue.ShutDown:
+          break
+
+    t1 = threading.Thread(target=producer)
+    t2 = threading.Thread(target=producer)
+    t3 = threading.Thread(target=consumer)
+
+    t1.start()
+    t2.start()
+    t3.start()
+
+    t1.join()
+    t2.join()
+    bq.shutdown()
+
+    t3.join()
+
+    self.assertEqual(len(received), 202)
+    self.assertEqual(sum(received), 2 * sum(range(101)))
+
+  def test_multithreading_timeout(self):
+    bq = ByteLimitedQueue(lambda x: x.weight(), maxsize=0, maxweight=10)
+    bq.put(FakeItem(10))
+
+    # The queue is completely full. A timeout put should raise queue.Full.
+    with self.assertRaises(queue.Full):
+      bq.put(FakeItem(5), timeout=0.01)
+
+    def delayed_consumer():
+      time.sleep(0.05)
+      bq.get()
+
+    # Start a thread that will free up space after 50ms.
+    t = threading.Thread(target=delayed_consumer)
+    t.start()
+
+    # The put should succeed once the consumer runs, use a high timeout to
+    # flakiness.
+    bq.put(FakeItem(5), timeout=60)
+    t.join()
+
+  def test_negative_timeout(self):
+    bq = ByteLimitedQueue(lambda x: x.weight())
+    # Putting an item with a negative timeout should raise ValueError.
+    with self.assertRaises(ValueError):
+      bq.put(FakeItem(5), timeout=-1)
+
+  def test_single_element_override(self):
+    bq = ByteLimitedQueue(lambda x: x.weight(), maxweight=10)
+    # An item of size 50 exceeds maxweight 10, but should be admitted
+    # immediately without blocking since the queue is currently empty!
+    bq.put(FakeItem(50), block=False)
+    self.assertEqual(bq.qsize(), 1)
+    self.assertEqual(bq.byte_size(), 50)
+
+  def test_inconsistent_weighing_fn(self):
+    # Return a different weight for the same item.
+    weights = [10, 5]
+    bq = ByteLimitedQueue(lambda x: weights.pop(0), maxweight=100)
+
+    bq.put(1)
+    self.assertEqual(bq.byte_size(), 10)
+
+    # Upon popping, the weighing function (if called) would have returned 5,
+    # but the stored weight prevents corruption and cleanly reduces the size to
+    # 0.
+    bq.get()
+    self.assertEqual(bq.byte_size(), 0)
+
+
+if __name__ == '__main__':
+  unittest.main()