The RISC-V port was just merged to Linux a few minutes ago. This means we will be in the 4.15 release, which should be out about 10 weeks from last Sunday. As soon as the tarballs are created, the RISC-V Linux ABI will be stable, and
since we’ll ideally be in a glibc release that comes out soon after that we’ll be fully ABI stable by early in February.
RISC-V is a completely free and open ISA that hasn’t seen much adoption just yet.