There is an object-capability model in the upcoming OCaml 5.0, however it's only in the Eio library, that deals with IO https://github.com/ocaml-multicore/eio#design-note-object-ca.... There's also Emily, a subset of OCaml based on POLA (Principle of Least Authority) https://www.hpl.hp.com/techreports/2006/HPL-2006-116.pdf. I'm unaware of any plain to extend OCaml in that direction though.