Dear OCaml users,

After two alpha releases, the release of OCaml 5.1.0 is drawing near.
We have thus released a first beta version of OCaml 5.1.0 to help you update your softwares and libraries ahead of the release (see below for the installation instructions).

Compared to the last alpha release, this beta contains two subtle internal runtime fixes, and one Windows fix.
Overall, the opam ecosystem looks in a good shape for the first beta release.

If you find any bugs, please report them on OCaml's issue tracker: https://github.com/ocaml/ocaml/issues.

Nearly all core development tools supports OCaml 5.1.0, and you can follow the last remaining wrinkles on the
opam readiness for 5.1.0 meta-issue: https://github.com/ocaml/opam-repository/issues/23669.

Currently, the release is planned for the end of July or the beginning of August.

If you are interested in full list of features and bug fixes of the new OCaml version, the
updated change log for OCaml 5.1.0 is available on GitHub: https://github.com/ocaml/ocaml/blob/5.1/Changes.

Happy hacking,
Florian Angeletti for the OCaml team.

Installation Instructions
------------------------------

The base compiler can be installed as an opam switch with the following commands
on opam 2.1:


   opam update
   opam switch create 5.1.0~beta1


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

* GitHub: https://github.com/ocaml/ocaml/archive/5.1.0-beta1.tar.gz
* OCaml archives at Inria: https://caml.inria.fr/pub/distrib/ocaml-5.1/ocaml-5.1.0~beta1.tar.gz

Fine-Tuned Compiler Configuration
----------------------------------------------

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> ocaml-variants.5.1.0~beta1+options <option_list>

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


    opam switch create 5.1.0~beta1+flambda+nffa ocaml-variants.5.1.0~beta1+options ocaml-option-flambda ocaml-option-no-flat-float-array

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

Changes since the last alpha release:
--------------------------------------------------

### Runtime System Bugfix

  - [#12037](https://github.com/ocaml/ocaml/issues/12037): Fix some data races by using volatile when necessary
    (Fabrice Buoro and Olivier Nicole, review by Guillaume Munch-Maccagnoni,
    Gabriel Scherer and Luc Maranget)

  - [#12253](https://github.com/ocaml/ocaml/issues/12253), [#12342](https://github.com/ocaml/ocaml/issues/12342): Fix infinite loop in signal handling.
    (Guillaume Munch-Maccagnoni, report by Thomas Leonard, review by
     KC Sivaramakrishnan and Sadiq Jaffer)

### Windows Bugfix

  - [#12184](https://github.com/ocaml/ocaml/issues/12184), [#12320](https://github.com/ocaml/ocaml/issues/12320): Sys.rename Windows fixes on directory corner cases.
    (Jan Midtgaard, review by Anil Madhavapeddy)