i tested the got-4o model 2024-08-06 with a chat completions call, the json_schema is working correctly. just wonder when you create the client, did you specify api_version as 2024-08-01-preview

client = AzureOpenAI(
  azure_endpoint = os.getenv("AZURE_OPENAI_ENDPOINT"),
  api_key= os.getenv("AZURE_OPENAI_API_KEY"),
  api_version="2024-08-01-preview"
)

assistant = client.beta.assistants.create(