diff --git a/pinecone/async_client/assistants.py b/pinecone/async_client/assistants.py
index 96b1aae7..a6ccc680 100644
--- a/pinecone/async_client/assistants.py
+++ b/pinecone/async_client/assistants.py
@@ -1783,6 +1783,7 @@ async def _chat_streaming(
             headers={"Content-Type": "application/json"},
             timeout=_stream_timeout(self._config.timeout, timeout),
         ) as response:
+            response.encoding = "utf-8-sig"
             async for line in response.aiter_lines():
                 if not line:
                     continue
@@ -1980,6 +1981,7 @@ async def _chat_completions_streaming(
             headers={"Content-Type": "application/json"},
             timeout=_stream_timeout(self._config.timeout, timeout),
         ) as response:
+            response.encoding = "utf-8-sig"
             async for line in response.aiter_lines():
                 if not line:
                     continue
diff --git a/pinecone/client/assistants.py b/pinecone/client/assistants.py
index 9fe49826..1c90217e 100644
--- a/pinecone/client/assistants.py
+++ b/pinecone/client/assistants.py
@@ -1890,6 +1890,7 @@ def _chat_streaming(
             headers={"Content-Type": "application/json"},
             timeout=_stream_timeout(self._config.timeout, timeout),
         ) as response:
+            response.encoding = "utf-8-sig"
             for line in response.iter_lines():
                 if not line:
                     continue
@@ -1948,6 +1949,7 @@ def _chat_completions_streaming(
             headers={"Content-Type": "application/json"},
             timeout=_stream_timeout(self._config.timeout, timeout),
         ) as response:
+            response.encoding = "utf-8-sig"
             for line in response.iter_lines():
                 if not line:
                     continue
diff --git a/tests/unit/test_assistant_stream_encoding.py b/tests/unit/test_assistant_stream_encoding.py
new file mode 100644
index 00000000..a9fa84da
--- /dev/null
+++ b/tests/unit/test_assistant_stream_encoding.py
@@ -0,0 +1,99 @@
+"""Assistant SSE streams decode UTF-8 and strip only the initial byte order mark."""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator, Iterator
+from typing import Any
+
+import httpx
+import orjson
+import pytest
+import respx
+
+from pinecone import AsyncPinecone, Pinecone
+
+BASE_URL = "https://api.test.pinecone.io"
+ASSISTANT_NAME = "stream-encoding"
+
+
+class ChunkedStream(httpx.SyncByteStream, httpx.AsyncByteStream):
+    def __init__(self, parts: list[bytes]) -> None:
+        self.parts = parts
+
+    def __iter__(self) -> Iterator[bytes]:
+        yield from self.parts
+
+    async def __aiter__(self) -> AsyncIterator[bytes]:
+        for part in self.parts:
+            yield part
+
+
+def _response(method: str, variant: str) -> tuple[httpx.Response, str]:
+    content = "你好 🌲\ufeff end"
+    if method == "chat":
+        chunk: dict[str, Any] = {
+            "type": "content_chunk",
+            "id": "chat-1",
+            "delta": {"content": content},
+        }
+    else:
+        chunk = {
+            "id": "chat-1",
+            "model": "gpt-4o",
+            "choices": [{"index": 0, "delta": {"content": content}}],
+        }
+    body = b"data: " + orjson.dumps(chunk) + b"\n\n"
+    if variant in ("bom", "split_bom", "bom_comment"):
+        body = b"\xef\xbb\xbf" + (b": heartbeat\n\n" if variant == "bom_comment" else b"") + body
+    elif variant in ("empty", "bom_empty"):
+        body, content = (b"\xef\xbb\xbf" if variant == "bom_empty" else b""), ""
+    elif variant in ("done", "bom_done"):
+        body = (b"\xef\xbb\xbf" if variant == "bom_done" else b"") + b"data: [DONE]\n\n" + body
+        content = ""
+    body += b"data: [DONE]\n\n"
+    parts = [body[:1], body[1:2], body[2:3], body[3:]] if variant == "split_bom" else [body]
+    return (
+        httpx.Response(
+            200, headers={"Content-Type": "text/event-stream"}, stream=ChunkedStream(parts)
+        ),
+        content,
+    )
+
+
+def _routes(router: respx.MockRouter, method: str, response: httpx.Response) -> None:
+    router.get(f"{BASE_URL}/assistant/assistants/{ASSISTANT_NAME}").respond(
+        json={"name": ASSISTANT_NAME, "status": "Ready", "host": BASE_URL}
+    )
+    suffix = "/chat/completions" if method == "chat_completions" else ""
+    router.post(f"{BASE_URL}/assistant/chat/{ASSISTANT_NAME}{suffix}").mock(return_value=response)
+
+
+@pytest.mark.parametrize("method", ["chat", "chat_completions"])
+@pytest.mark.parametrize(
+    "variant",
+    ["plain", "bom", "split_bom", "bom_comment", "empty", "done", "bom_empty", "bom_done"],
+)
+def test_sync_stream_encoding(method: str, variant: str) -> None:
+    response, expected = _response(method, variant)
+    with respx.mock() as router, Pinecone(api_key="test-key", host=BASE_URL) as pc:
+        _routes(router, method, response)
+        stream = getattr(pc.assistants, method)(
+            assistant_name=ASSISTANT_NAME, messages=[{"content": "hello"}], stream=True
+        )
+        assert stream.collect() == expected
+
+
+@pytest.mark.parametrize("method", ["chat", "chat_completions"])
+@pytest.mark.parametrize(
+    "variant",
+    ["plain", "bom", "split_bom", "bom_comment", "empty", "done", "bom_empty", "bom_done"],
+)
+async def test_async_stream_encoding(method: str, variant: str) -> None:
+    response, expected = _response(method, variant)
+    with respx.mock() as router:
+        _routes(router, method, response)
+        async with AsyncPinecone(api_key="test-key", host=BASE_URL) as pc:
+            stream = await getattr(pc.assistants, method)(
+                assistant_name=ASSISTANT_NAME, messages=[{"content": "hello"}], stream=True
+            )
+            assert await stream.collect() == expected