Try MUMPS, widely used but little training data online. Probably less than some esolangs

Frontier models have gotten much better at ObjectScript (the InterSystems evolution of MUMPS/M).

Palindrome:

https://chatgpt.com/s/t_69bc8d8c116c8191a339a33f0fbcc935

This is a noticeable improvement from a year ago.

I wish it would use Return instead of Quit but that’s a stochastic parrot for you.