I recently found this paper: BebopNet: Deep Neural Models for Personalized Jazz Improvisations, by Shunit Haviv Hakimi, Nadav Bhonker, Ran El-Yaniv from the Technion. It uses deep learning approach to teach a machine to improvise when playing Jazz. The paper won the best paper award at ISMIR 2020.
The results are pretty cool. The level of improvisation is pretty good but I hear a little awkwardness in the timing of the notes.