ch1 h-structured running issue

[dapeng09]

llm = ChatOpenAI(model="gpt-3.5", temperature=0)
using gpt-3.5 gives 404 error
openai.NotFoundError: Error code: 404 - {'error': {'message': 'The model gpt-3.5 does not exist or you do not have access to it.', 'type': 'invalid_request_error', 'param': None, 'code': 'model_not_found'}}

so I turn to gpt-4o
llm = ChatOpenAI(model="gpt-4o", temperature=0)
then the output is
answer='A pound of bricks and a pound of feathers weigh the same.' justification='The question is a classic example of a riddle that plays on the perception of weight and volume. Both a pound of bricks and a pound of feathers weigh exactly one pound.'

This is not the json format we expected, right? there is no curly braces. So what's going on here?
my package version like:
langchain 0.3.26
langchain-community 0.3.26
langchain-core 0.3.66
langchain-openai 0.3.18
langchain-postgres 0.0.14
langchain-text-splitters 0.3.8