OCaml 4.11.0, second beta release

The release of OCaml 4.11.0 is approaching.
As one step further in this direction, we have published a second beta
release. This new release fixes an MSVC-specific runtime issue.

The compatibility of the opam ecosystem with OCaml 4.11.0 is currently quite
good with only 7 packages not currently available, and it should be possible to
test this beta without too much trouble.

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.4.11.0+beta2 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git


opam switch create ocaml-variants.4.11.0+beta2+<VARIANT> --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

where you replace <VARIANT> with one of these: afl, flambda, fp, fp+flambda

We would love to hear about any bugs. Please report them here:

If you are interested by the list of new features, and the on-going list
of bug fixes the updated change log for OCaml 4.11.0 is available at:


Compared to the previous beta release, the exhaustive list of changes
is as follows:


  • #9714, #9724: Use the C++ alignas keyword when compiling in C++.
    Fixes a bug with MSVC C++ 2015/2017. Add a terminator to the
    caml_domain_state structure to better ensure that members are
    correctly spaced.
    (Antonin Décimo, review by David Allsopp and Xavier Leroy)

Manual and documentation

  • #8644: fix formatting comment about @raise in stdlib’s mli files
    (Élie Brami, review by David Allsopp)

  • #9712: Update the version format to allow “~”.
    The new format is “major.minor[.patchlevel][(+|~)additional-info]”,
    for instance “4.12.0~beta1+flambda”.
    This is a documentation-only change for the 4.11 branch, the new format
    will be used starting with the 4.12 branch.
    (Florian Angeletti, review by Damien Doligez and Xavier Leroy)