Chat.system_prompt

>>> chat = session.chat
>>> print(chat.system_prompt)  
You are a UI assistant.
You have access to an OLAP cube to perform data analysis.
...

>>> from os import linesep
>>> chat.system_prompt = (
...     f"{chat.system_prompt}{linesep}Always answer in French."
... )
>>> print(chat.system_prompt)  
You are a UI assistant.
...
Always answer in French.

>>> chat.system_prompt = "Only answer questions about the data model."
>>> print(chat.system_prompt)
Only answer questions about the data model.