The most important thing to know about this implementation is that it's based on split circa 2013, which is old but happens to be the version that ships with MacOS.
Maybe someday! Honestly I can't recommend it, just use the current version of split and csplit in the GNU coreutils (repo).
Usage: splirst [OPTIONS] <FILE_PATH> [PREFIX]
Arguments:
<FILE_PATH>
[PREFIX] [default: x]
Options:
-a, --suffix-length <SUFFIX_LENGTH> [default: 2]
-d, --numeric-suffix
-l, --line-count <LINE_COUNT> [default: 1000]
-n, --chunk-count <CHUNK_COUNT>
-b, --byte-count <BYTE_COUNT>
-p, --pattern <PATTERN>
-h, --help Print help