opam 2.0 Beta is out!

Authors: Louis Gesbert
Date: 2017-02-09
Category: Tooling
Tags: opam

UPDATE (2017-02-14): A beta2 is online, which fixes issues and performance of the opam build command. Get the new binaries, or recompile the opam-devel package and replace the previous binary.

We are pleased to announce that the beta release of opam 2.0 is now live! You can try it already, bootstrapping from a working 1.2 opam installation, with:

opam update; opam install opam-devel

With about a thousand patches since the last stable release, we took the time to gather feedback after our last announcement and implemented a couple of additional, most-wanted features:

There are many more features, like the new opam clean and opam admin commands, a new archive caching system, etc., but we'll let you check the full changelog.

We also improved still on the already announced features, including compilers as packages, local switches, per-switch repository configuration, package file tracking, etc.

The updated documentation is at http://opam.ocaml.org/doc/2.0/. If you are developing in opam-related tools, you may also want to browse the new APIs.

Try it out

Please try out the beta, and report any issues or missing features. You can:

Some users have been using the alpha for the past months without problems, but you may want to keep your opam 1.2 installation intact until the release is out. An easy way to do this is with an alias:

alias opam2="OPAMROOT=~/.opam2 path/to/opam-2-binary"

Changes to be aware of

Command-line interface

As before, opam is self-documenting, so be sure to check opam COMMAND --help first when in doubt. The bash completion scripts have also been thoroughly improved, and may help navigating the new options.


There are both a few changes (extensions, mostly) to the package description format, and more drastic changes to the repository format, mainly related to translating the old compiler definitions into packages.

The official opam repository at https://opam.ocaml.org remains in 1.2 format for now, but has a live-updated 2.0 mirror to which you should be automatically redirected. It cannot yet accept package definitions in 2.0 format.

Package format

The full, up-to-date specification of the format can be browsed in the manual.

Repository format

In the official, default repository, and also when migrating repositories from older format versions, there are:

The layout is otherwise the same, apart from:


Thanks for trying out the beta! Please let us have feedback, preferably to the opam tracker; other options include the opam-devel list and #opam IRC channel on Freenode.

About OCamlPro:

OCamlPro is a R&D lab founded in 2011, with the mission to help industrial users benefit from state-of-the art programming languages like OCaml and Rust.

We design, create and implement custom ad-hoc software for our clients. We also have a long experience in developing and maintaining open-source tooling for OCaml, such as Opam, TryOCaml, ocp-indent, ocp-index and ocp-browser, and we contribute to the core-development of OCaml, notably with our work on the Flambda optimizer branch.

Another area of expertise is that of Formal Methods, with tools such as our SMT Solver Alt-Ergo (check our Alt-Ergo Users'). We also provide vocational trainings in OCaml and Rust, and we can build courses on formal methods on-demand. Do not hesitate to reach out by email: contact@ocamlpro.com.