diff --git a/assemblyai/tts/v1/models.py b/assemblyai/tts/v1/models.py
index bdebdbd..245f0de 100644
--- a/assemblyai/tts/v1/models.py
+++ b/assemblyai/tts/v1/models.py
@@ -247,7 +247,10 @@ class TTSResponseInfo(BaseModel):
 
     billed_characters: Optional[int] = None
     """The characters the request bills. On a stream, the value as the stream
-    started: a body cut by a server failure bills nothing."""
+    started: a body cut by a server failure bills nothing, one cut by
+    `session_expired` (the API's 600-second limit) bills the text before the
+    sentence being spoken, and one cut by `audio_backlog` (a client reading
+    too slowly) bills every character."""
 
     audio_duration_ms: Optional[int] = None
     """The duration of the audio in milliseconds, on a complete response:
diff --git a/tests/unit/test_tts.py b/tests/unit/test_tts.py
index 0c985cd..32b7e74 100644
--- a/tests/unit/test_tts.py
+++ b/tests/unit/test_tts.py
@@ -320,6 +320,33 @@ def test_a_refused_stream_releases_its_connection():
     assert body.closed
 
 
+class _CutJsonBody(httpx.SyncByteStream):
+    closed = False
+
+    def __iter__(self) -> Iterator[bytes]:
+        yield b'{"code": '
+        raise httpx.ReadError("connection reset")
+
+    def close(self) -> None:
+        self.closed = True
+
+
+def test_a_refused_stream_releases_its_connection_if_its_body_fails():
+    # httpx closes a fully read body itself; a body cut while it is read is
+    # released only by the stream. The error stays referenced until the end,
+    # as a caller that logs it would, so its traceback keeps the stream's
+    # frames alive and garbage collection cannot release the body instead.
+    body = _CutJsonBody()
+    with httpx.Client(transport=_transport(body, status=503)) as http:
+        speech = api.stream_speech(
+            http, base_url="https://tts.test", body={"text": "Hi."}, timeout=5.0
+        )
+        with pytest.raises(httpx.ReadError) as exc_info:
+            speech.read()
+        assert body.closed
+        assert "connection reset" in str(exc_info.value)
+
+
 def test_a_client_built_from_api_key_is_closed_with_the_instance():
     with aai.TextToSpeech(api_key="k") as tts:
         http = tts.client.http_client
diff --git a/tests/unit/test_tts_async.py b/tests/unit/test_tts_async.py
index 23b3f1e..876d993 100644
--- a/tests/unit/test_tts_async.py
+++ b/tests/unit/test_tts_async.py
@@ -187,6 +187,33 @@ async def test_a_refused_stream_releases_its_connection():
     assert body.closed
 
 
+class _CutJsonBody(httpx.AsyncByteStream):
+    closed = False
+
+    async def __aiter__(self) -> AsyncIterator[bytes]:
+        yield b'{"code": '
+        raise httpx.ReadError("connection reset")
+
+    async def aclose(self) -> None:
+        self.closed = True
+
+
+async def test_a_refused_stream_releases_its_connection_if_its_body_fails():
+    # httpx closes a fully read body itself; a body cut while it is read is
+    # released only by the stream. The error stays referenced until the end,
+    # as a caller that logs it would, so its traceback keeps the stream's
+    # frames alive and garbage collection cannot release the body instead.
+    body = _CutJsonBody()
+    async with httpx.AsyncClient(transport=_transport(body, status=503)) as http:
+        speech = async_api.stream_speech(
+            http, base_url="https://tts.test", body={"text": "Hi."}, timeout=5.0
+        )
+        with pytest.raises(httpx.ReadError) as exc_info:
+            await speech.aread()
+        assert body.closed
+        assert "connection reset" in str(exc_info.value)
+
+
 async def test_an_owned_pool_is_closed_on_aclose():
     tts = aai.AsyncTextToSpeech(api_key="k")
     http = tts.client.http_client