OCaml 4.10.0, first beta

The release of OCaml 4.10.0 is approaching. We have published
a first beta version to help you adapt your software to the new features
ahead of the release.

During our preliminary tests for this new beta, we discovered that the recent
work towards a multicore-ready OCaml runtime introduced compatibility issues
within some opam packages, that were tweaking the runtime internals.
Most of those opam packages have been fixed, or will be soon.
Nevertheless, if you are affected by such compatibility issue, please speak up.

The source code is available at these addresses:


The compiler can also be installed as an OPAM switch with one of the
following commands.

opam switch create ocaml-variants.4.10.0+beta1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git


opam switch create ocaml-variants.4.10.0+beta1+<VARIANT> --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

where you replace <VARIANT> with one of these:

We want to know about all bugs. Please report them here:


Happy hacking.


Second link corrected:


Indeed. Fixed, thanks!

For the people wanting to give OCaml 4.10.0beta1 a shot, here is an opam overlay which adds fixes to major packages for them to work with this beta: https://github.com/kit-ty-kate/opam-alpha-repository

To use it, simple call:

$ opam switch 4.10.0+beta1
$ opam repository add alpha git://github.com/kit-ty-kate/opam-alpha-repository.git

Obviously, this repository should not be used in production and probably contains a few bugs, but at least it allows everyone to have almost as many packages available as with OCaml 4.09. Only 60ish packages are still not available, but apart from the notable exception of merlin all the essential packages and dependencies are there.

This work has been part of the release-readyness effort founded by the OCaml Software Foundation as announced here: [ANN] the OCaml Software Foundation

The rest of the effort is going to be put towards having merlin available for OCaml 4.10 and upstreaming all the fixes from opam-alpha-repository (most of them have PRs associated already). Iā€™m hopeful for them be all upstreamed and available before the stable release of OCaml 4.10.