update token limit

app.py

@@ -19,6 +19,7 @@ os.environ["OPENAI_API_KEY"] = os.environ["OPENAI_TOKEN"]
 #model = 'gpt-3.5-turbo'
 model = 'gpt-3.5-turbo-16k'
 #model = 'gpt-4'
+token_limit = 4000 if model == 'gpt-3.5-turbo' else 16000
 temperature = 0
 llm = ChatOpenAI(temperature=temperature, model=model)
 
@@ -36,7 +37,7 @@ qa = RetrievalQAWithSourcesChain.from_chain_type(
             retriever=vectorstore.as_retriever(search_type="mmr"),
             #retriever=vectorstore.as_retriever(),
             return_source_documents=True, 
-            max_tokens_limit=4000
+            max_tokens_limit=token_limit
         )
 
 # Define tools