Financial software is the one of the last ones that I want to be written by LLMs, as long as they claim that loading a 10GB file into memory instead of reading it line by line is memory efficient
LLMs can be used to make software more robust and more secure. You can ask the very best LLM like o3 Pro, give it a lot of time, to look for potential security issues and bugs in the code. You can ask them to write extremely stringent unit tests.
And finally, humans should obviously review all the code in any critical system.