[limsup]

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.

[TomVDB]

The RISC-V compressed instructions are more a shorthand for some commonly used 32-bit instructions than a 16-bit ISA that stands on its own: the compressed instructions lack a number of essential operations that make it impractical to only use compressed instructions

This is in contrast to, say, the ARM Thumb instructions, where you can can have entirely libraries that use 16-bit instruction without ever needing a 32-bit one.

[messe]

That's not what this is. That's just shorter versions of several common instructions to increase code density, not a 16-bit ISA.