To add, in the case of RISC-V, the base integer ISA and most of the core extensions use fixed length 32-bit encoding (RV32/64 E/IMFAD). The basic encoding, however, allows for shorter and longer instructions in 16 bit increments. There is also the compressed ISA extension that encodes a subset of IMFAD into 16 bit instructions. The per-byte dynamic code size of the compressed extension ends up being on par with x86/x64 and Thumb2.