The base instruction set is tiny but there are quite a few extensions and pretty much every practical implementation includes at least a few of them. i.e. the

The base instruction set is tiny but there are quite a few extensions and pretty much every practical implementation includes at least a few of them. i.e. the GD32V microcontrollers implement RV32IMAC, Allwinner D1 which is a "full-blown" CPU meant to run Linux implements RV64IMAFDCVU. RV32I/RV64I are the base 32/64 bit integer instruction sets and every letter after that is a different extension. Most of the extensions are relatively small and simple, but the C (compressed instructions) extension introduces some decoder complexity and the V (vector) extension adds several hundred instructions. Though even with all the extensions it is still a very small/simple ISA by modern standards.