No, there is a 16-bit version
https://content.riscv.org/wp-content/uploads/2017/05/riscv-s... See chapter 12, “C” Standard Extension for
Compressed Instructions
> This chapter describes the current draft proposal for the RISC-V standard compressed instruction set extension, named “C”, which reduces static and dynamic code size by adding short 16-bit instruction encodings for common operations.