I’m not sure if this area is a work in progress but it used to work so there is a regression. I’m reporting it here in case dev team is not aware of it.
If you have a scene with hair curves (for instance as particles on a mesh), the Hair Info node sockets
Length yield 0 when GPU is on. With CPU, everything works properly.
Tested on Ubuntu, Quadro graphic card and latest commit (f6b73966101db0fef10abd7b3a18e4a1ca120013)