Hi y’all,
I’m happy to announce that containers 3.9 has just been released. Containers is a lightweight, modular extension of the stdlib that tries to remains compatible with it.
Containers is starting to sprout some serialization primitives: it now has codecs for Bencode and CBOR. This release also contains a revamp of the testlib system (bye qtest) and the use of ocamlformat, for potential contributors who enjoy that. Containers should also be compatible with OCaml 5.0.
Documentation here
Cheers! 
edit: added links 