The Stick is the perfect vehicle for improvising. Being able to alter the harmonic and rhythmic setting at any moment, as well as having different sonic pallets for each hand. Plus the immediacy of having your fingers right on the strings...
Keyboards are great and so is the guitar, but only one type of instrument lets you do it all with such complete integration and expressive immediacy...
I'd only been playing for 2 years when I released my first improv recording with Tim Reynolds
Stick and Stones: a collection of spontaneous improvisations. I'm probably proudest of
Water on the Moon (1998), though
AZUL was a pretty fun session as well. There are very few long-form solo improv recordings out there on any instrument... (Keith Jarrett's
Köln Concert comes to mind... any others you can think of?)
If you haven't checked out WOTM, please do. Here is is as one uninterrputed hour-long piece on bandcamp...
https://greghoward.bandcamp.com/album/water-on-the-moon