OCaml 4.13.0, first alpha release

Three months after the release of OCaml 4.12.0, the set of new features for the future version 4.13.0 of OCaml has been frozen. I am thus happy to announce the first alpha release for OCaml 4.13.0 .

This alpha version is here to help fellow hackers join us early in our bug hunting and opam ecosystem fixing fun (see below for the installation instructions). You can see the progress on this front at

If you find any bugs, please report them here:

Once most major OCaml tools are supported, we will switch to beta releases.
The full release is expected to happen in September.

If you are interested by the ongoing list of new features and bug fixes, the
updated change log for OCaml 4.13.0 is available at:

Note that there is still some on-going work to support improved polling points in preparation
for OCaml multicore. Another alpha release will be published once this work is merged.

Installation instructions

The base compiler can be installed as an opam switch with the following commands

opam update
opam switch create 4.13.0~alpha1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

If you want to tweak the configuration of the compiler, you can switch to the option variant with:

opam update
opam switch create <switch_name> --packages=ocaml-variants.4.13.0~alpha1+options,<option_list> --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

where <option_list> is a comma separated list of ocaml-option-* packages. For instance, for a flambda and no-flat-float-array switch:

opam switch create 4.13.0~alpha1+flambda+nffa --packages=ocaml-variants.4.13.0~alpha1+options,ocaml-option-flambda,ocaml-option-no-flat-float-array --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

All available options can be listed with “opam search ocaml-option”.

If you want to test this version, it is advised to install the alpha opam repository at


opam repo add alpha git://github.com/kit-ty-kate/opam-alpha-repository.git

This alpha repository contains various fixes in the process of being upstreamed.

The source code for the alpha is also available at these addresses:



This might sound a bit silly but among other things, I’m really excited for String.starts_with, String.ends_with and the new Array functions :+1: