diff --git a/langfuse/openai.py b/langfuse/openai.py
index d7e250444..d780e0de1 100644
--- a/langfuse/openai.py
+++ b/langfuse/openai.py
@@ -460,7 +460,7 @@ def _parse_usage(usage=None):
     if usage is None:
         return
 
-    usage_dict = usage.copy() if isinstance(usage, dict) else usage.__dict__
+    usage_dict = usage.copy() if isinstance(usage, dict) else usage.__dict__.copy()
 
     for tokens_details in ["prompt_tokens_details", "completion_tokens_details"]:
         if tokens_details in usage_dict and usage_dict[tokens_details] is not None:
diff --git a/tests/test_openai.py b/tests/test_openai.py
index 5dc991ef4..31176bfae 100644
--- a/tests/test_openai.py
+++ b/tests/test_openai.py
@@ -70,7 +70,7 @@ def test_openai_chat_completion():
         {"content": "1 + 1 = ", "role": "user"},
     ]
     assert generation.data[0].type == "GENERATION"
-    assert generation.data[0].model == "gpt-3.5-turbo-0125"
+    assert "gpt-3.5-turbo-0125" in generation.data[0].model
     assert generation.data[0].start_time is not None
     assert generation.data[0].end_time is not None
     assert generation.data[0].start_time < generation.data[0].end_time
@@ -135,7 +135,7 @@ def test_openai_chat_completion_stream():
 
     assert generation.data[0].input == [{"content": "1 + 1 = ", "role": "user"}]
     assert generation.data[0].type == "GENERATION"
-    assert generation.data[0].model == "gpt-3.5-turbo-0125"
+    assert "gpt-3.5-turbo-0125" in generation.data[0].model
     assert generation.data[0].start_time is not None
     assert generation.data[0].end_time is not None
     assert generation.data[0].start_time < generation.data[0].end_time
@@ -536,7 +536,7 @@ def test_openai_completion():
     assert completion.choices[0].text == generation.data[0].output
     assert generation.data[0].input == "1 + 1 = "
     assert generation.data[0].type == "GENERATION"
-    assert generation.data[0].model == "gpt-3.5-turbo-instruct"
+    assert "gpt-3.5-turbo-instruct" in generation.data[0].model
     assert generation.data[0].start_time is not None
     assert generation.data[0].end_time is not None
     assert generation.data[0].start_time < generation.data[0].end_time
@@ -587,7 +587,7 @@ def test_openai_completion_stream():
 
     assert generation.data[0].input == "1 + 1 = "
     assert generation.data[0].type == "GENERATION"
-    assert generation.data[0].model == "gpt-3.5-turbo-instruct"
+    assert "gpt-3.5-turbo-instruct" in generation.data[0].model
     assert generation.data[0].start_time is not None
     assert generation.data[0].end_time is not None
     assert generation.data[0].start_time < generation.data[0].end_time