I would not expect an LLM to be good at this without specialized training. I have tried prompting for code generation.
I do not know of LLMs that have been specifically trained on, say, the testing corpus of some "lint" programs and against known vulns. As you point out, it wouldn't be possible as a user of an LLM AI to do the equivalent by showing it some vulns, while it would be perfectly reasonable to get an LLM to write, for example, business case studies by showing it examples.
I don't think specialized training solves any of the problems I mentioned. It doesn't increase the window size, or provide any of the types of highly specialized and optimized multi-file, multi-technique analysis, or make it any cheaper.
I do not know of LLMs that have been specifically trained on, say, the testing corpus of some "lint" programs and against known vulns. As you point out, it wouldn't be possible as a user of an LLM AI to do the equivalent by showing it some vulns, while it would be perfectly reasonable to get an LLM to write, for example, business case studies by showing it examples.