diff --git a/etc/unittest/client.py b/etc/unittest/client.py
index 2bc00c2e..ec8aa4b7 100644
--- a/etc/unittest/client.py
+++ b/etc/unittest/client.py
@@ -35,13 +35,15 @@ class TestPassModel(unittest.TestCase):
         response = client.chat.completions.create(messages, "Hello", stream=True)
         for chunk in response:
             self.assertIsInstance(chunk, ChatCompletionChunk)
-            self.assertIsInstance(chunk.choices[0].delta.content, str)
+            if chunk.choices[0].delta.content is not None:
+                self.assertIsInstance(chunk.choices[0].delta.content, str)
         messages = [{'role': 'user', 'content': chunk} for chunk in ["You ", "You ", "Other", "?"]]
         response = client.chat.completions.create(messages, "Hello", stream=True, max_tokens=2)
         response = list(response)
-        self.assertEqual(len(response), 2)
+        self.assertEqual(len(response), 3)
         for chunk in response:
-            self.assertEqual(chunk.choices[0].delta.content, "You ")
+            if chunk.choices[0].delta.content is not None:
+                self.assertEqual(chunk.choices[0].delta.content, "You ")
 
     def test_stop(self):
         client = Client(provider=YieldProviderMock)
diff --git a/g4f/api/__init__.py b/g4f/api/__init__.py
index 9033aafe..d1e8539f 100644
--- a/g4f/api/__init__.py
+++ b/g4f/api/__init__.py
@@ -6,7 +6,7 @@ import nest_asyncio
 from fastapi           import FastAPI, Response, Request
 from fastapi.responses import StreamingResponse, RedirectResponse, HTMLResponse, JSONResponse
 from pydantic          import BaseModel
-from typing            import List
+from typing            import List, Union
 
 import g4f
 import g4f.debug
@@ -16,12 +16,12 @@ from g4f.typing import Messages
 class ChatCompletionsConfig(BaseModel):
     messages: Messages
     model: str
-    provider: str | None 
+    provider: Union[str, None] 
     stream: bool = False
-    temperature: float | None 
+    temperature: Union[float, None] 
     max_tokens: int = None
-    stop: list[str] | str | None
-    access_token: str | None
+    stop: Union[list[str], str, None]
+    access_token: Union[str, None]
 
 class Api:
     def __init__(self, engine: g4f, debug: bool = True, sentry: bool = False,
diff --git a/g4f/client.py b/g4f/client.py
index b44a5230..023d53f6 100644
--- a/g4f/client.py
+++ b/g4f/client.py
@@ -17,7 +17,7 @@ from . import get_model_and_provider, get_last_provider
 
 ImageProvider = Union[BaseProvider, object]
 Proxies = Union[dict, str]
-IterResponse = Generator[ChatCompletion | ChatCompletionChunk, None, None]
+IterResponse = Generator[Union[ChatCompletion, ChatCompletionChunk], None, None]
 
 def read_json(text: str) -> dict:
     """
@@ -124,7 +124,7 @@ class Completions():
         stream: bool = False,
         response_format: dict = None,
         max_tokens: int = None,
-        stop: list[str] | str = None,
+        stop: Union[list[str], str] = None,
         **kwargs
     ) -> Union[ChatCompletion, Generator[ChatCompletionChunk]]:
         if max_tokens is not None:
diff --git a/g4f/stubs.py b/g4f/stubs.py
index b9934b8c..49cf8a88 100644
--- a/g4f/stubs.py
+++ b/g4f/stubs.py
@@ -1,6 +1,8 @@
 
 from __future__ import annotations
 
+from typing import Union
+
 class Model():
     ...
 
@@ -52,7 +54,7 @@ class ChatCompletionChunk(Model):
         }
 
 class ChatCompletionMessage(Model):
-    def __init__(self, content: str | None):
+    def __init__(self, content: Union[str, None]):
         self.role = "assistant"
         self.content = content
 
@@ -72,7 +74,9 @@ class ChatCompletionChoice(Model):
         }
 
 class ChatCompletionDelta(Model):
-    def __init__(self, content: str | None):
+    content: Union[str, None] = None
+
+    def __init__(self, content: Union[str, None]):
         if content is not None:
             self.content = content
 
@@ -80,7 +84,7 @@ class ChatCompletionDelta(Model):
         return self.__dict__
 
 class ChatCompletionDeltaChoice(Model):
-    def __init__(self, delta: ChatCompletionDelta, finish_reason: str | None):
+    def __init__(self, delta: ChatCompletionDelta, finish_reason: Union[str, None]):
         self.delta = delta
         self.finish_reason = finish_reason