BSD licenses
The RISC-V authors and their institution originally sourced the ISA documents and several CPU designs under BSD licenses, which allow derivative works—such as RISC-V chip designs—to be either open and free, or closed and proprietary. The ISA specification itself (i.e., the encoding of the instruction set) was published in 2011 as open source with all rights reserved. The actual technical report (an expression of the specification) was later placed under a Creative Commons license to permit enhancement by external contributors through the RISC-V Foundation, and later RISC-V International.