The bindings are contained in findlib package lz4.
To roundtrip some data:
let data = "wild wild fox" in
let compressed = LZ4.Bytes.compress (Bytes.of_string data) in
let decompressed = LZ4.Bytes.decompress ~length:(String.length data) compressed in
Printf.printf "%S\n" (Bytes.to_string decompressed) (* => "wild wild fox" *)
Documentation
The API documentation is available at GitHub pages.