RISC-V has two sorts of extensions. The custom extensions I mentioned in my post above are vendor-specific and they can do what they want, patent them, keep th

RISC-V has two sorts of extensions. The custom extensions I mentioned in my post above are vendor-specific and they can do what they want, patent them, keep them secret, whatever. However the standard extensions which go through ratification by RISC-V International and are meant to be implemented by anyone must have a royalty-free patent grant (see: https://riscv.org/wp-content/uploads/2022/03/RISC-V-Amended-Internal-Regulations-APPROVED-2022-Feb-17.pdf https://riscv.org/wp-content/uploads/2022/03/RISC-V-Amended-...)