OCaml Changelog

Dune 3.23.0

2026-05-05T00:00:00-00:00

The Dune team is pleased to announce the release of dune 3.23.0.

Along with many other fixes and improvements, some highlights include:

Add support for c_library_flags in foreign_stubs (#13484, @madroach)
Many improvements to the promotion and diffing functionality, by @rgrinberg.
As part of the previous, a breaking change to the promotion logic has been introduced: Dune does not automatically promote generated opam files, which must now be manually promoted with dune promote. You can trigger building .opam files with the @install, @runtest, and @opam aliases. In release mode, .opam files aren't generated at all and whatever is in the source is used (ocaml/dune#14108, @rgrinberg).
User rules and inline test runners are now sandboxed by default (ocaml/dune#13805 and ocaml/dune#14257, @rgrinberg).
The minimum OCaml version required to build dune is now 4.14.

See the full changelog for all new features and fixes, and for attribution to the contributors who made it all possible. Thank you, contributors!

If you encounter a problem with this release, please report it in our issue tracker.

Odoc 3.2.0

2026-05-01T00:00:00-00:00

CHANGES:

Added

Allow persistent latex macros in HTML/KaTeX backend (@dlesbre, #1391)
markdown-generate command now accepts multiple .odocl files in a single
invocation, eliminating the need for shell scripting (@davesnx, #1387)
Support for OxCaml (@lukemaurer, @art-w, #1399)
OCaml 5.5.0 support (@panglesd, @xvw, #1406)

Fixed

Fix compile-time crashing bugs #930 and #1385 (@jonludlam, #1400)
Markdown backend assumes ocaml as langId on declarations
Markdown backend collects all code snippets and render a single code block with comments, rather than split the variants/records per constructor/field
Fix URL remapping for page references (@jonludlam, #1395)
Fix #1396, which broke incrememntal builds (@jonludlam, #1402)
Ensure all warnings turn into errors with --warn-error (@jonludlam, #1402)
Fix missing parentheses for polymorphic arguments (@art-w, #1404)

Merlin 5.7.1-504

2026-04-30T00:00:00-00:00

CHANGES:

Thu Apr 30 14:15:42 CEST 2026

merlin library
- Fix a cache invalidation issue due to the introduction of hidden deps in
  OCaml 5.2. (#2062)
index format
- Merged indexes now point to each-others. This results in smaller index
  files. The index of a project is now defined by all its index files, not
  only the final aggregation. (#2051)

opam 2.5.1

2026-04-16T00:00:00-00:00

Feedback on this post is welcomed on Discuss!

We are pleased to announce the release of opam 2.5.1 fixing a security issue (OSEC-2026-03) and other minor things.

We advise everyone to upgrade. Please read on for installation and upgrade instructions.

Security fix

OSEC-2026-03: Invalidate .install fields containing destination filepath trying to escape their scope. Thanks to @andrew for reporting this issue. (#6897)

Distributions maintainers that have not already done so, are invited to either upgrade their opam package to 2.5.1 or backport the fix. For any questions please send an email to the authors of this here blog post as listed above.

Other changes

Fix a string injection from the depexts field to nix-build, when os-family=nixos. Thanks to @RyanGibb for this contribution and @andrew for the report. (#6894)
Restore the distribution detection on Gentoo. (#6887)
Add support for single-quoted values of the /etc/os-release file. (#6887)
Fix rare potential GC corruptions. Thanks to @avsm for the contribution and @andrew for the report. (#6882, #6880)

Try it

The upgrade instructions are unchanged:

Either from binaries: run

For Unix systems

bash -c "sh <(curl -fsSL https://opam.ocaml.org/install.sh) --version 2.5.1"

or from PowerShell for Windows systems

Invoke-Expression "& { $(Invoke-RestMethod https://opam.ocaml.org/install.ps1) } -Version 2.5.1"

or download manually from the Github "Releases" page to your PATH.

Or from source, manually: see the instructions in the README.

You should then run:

opam init --reinit -ni

Please report any issues to the bug-tracker.

Happy hacking!

Dune 3.22.2

2026-04-14T00:00:00-00:00

The Dune team is pleased to announce the release of dune 3.22.2.

This is a patch release consisting of bug fixes. See the full changelog for all the changes and for attribution to the contributors who made it all possible. Thank you, contributors!

If you encounter a problem with this release, please report it in our issue tracker.

OCaml-LSP 1.26.0

2026-04-10T00:00:00-00:00

This new release of OCaml-LSP brings several new features and improvements, including new custom requests, support for range formatting, and enhanced hover capabilities.

See the related announcement on the Discuss forums.

Merlin 5.7.0-504

2026-04-10T00:00:00-00:00

We're happy to announce the release of Merlin 5.7.0-504. This release comes with a number of bug fixes and improvements to Merlin.

For more details, we encourage you to delve into the full changelog.

See the related announcement on the Discuss forums.

Merlin 5.7.0-504

2026-04-09T00:00:00-00:00

CHANGES:

Thu Apr 09 09:59:38 WAT 2026

merlin library
- Implement new refactor-extract-region command for extracting region to a fresh let binding (warning: this feature is still experimental) (#1948)
- Add "Other" variant to locate-types result (#2025)
- Don't include option in locate-types result for optional parameters (#2027)
- Fix record field autocompletion (#2028)
- Signature help should not loop over the parameters once it is finished (#2023)
- Fix bugs on signature help about labelled and optional parameters (#2032)
- Add -end-position parameter for enclosing (#2029)
- Signature help should appear even if the 'in' is not written (#2036)
- Improve type enclosing behavior on various class and object related items
  (#2053)
merlin binary
- Define PATH_MAX to 4096 if undefined (eg. hurd) (#2039)
test suite
- Add a reproduction case for #1214, the issue has been resolved before (#2022)
- Add reproduction case for #1763 but it is not failing anymore (#2021)
- Add a test to reproduce Locate command fails on multi-line type definitions (#2020)
- Add a regression test for issue #2019 (#2030)

Dune 3.22.1

2026-04-06T00:00:00-00:00

The Dune team is pleased to announce the release of dune 3.22.1.

This is a patch release consisting of bug fixes. See the full changelog for all the changes and for attribution to the contributors who made it all possible. Thank you, contributors!

If you encounter a problem with this release, please report it in our issue tracker.

Utop 2.17.0

2026-03-26T00:00:00-00:00

CHANGES:

Add support for OCaml 5.5 (#510 @anmonteiro)
Add support for neocaml or other major modes in utop.el (#511, @bbatsov)

Dune-release 2.2.1

2026-03-26T00:00:00-00:00

CHANGES:

Added

Add support for marking a release as a prerelease. (#517, @Sudha247)

Mdx 2.5.2

2026-03-23T00:00:00-00:00

CHANGES:

Added

Support OCaml 5.5 (#475, @anmonteiro)

Ppxlib 0.38.0

2026-03-20T00:00:00-00:00

The ppxlib team is happy to announce the release of ppxlib.0.38.0.

The main features of this release are support for OCaml 5.5 and improved support of OCaml 5.4 and 5.3. It also comes with a few bug fixes and a couple new API entries, you can read the extensive release notes here.

This is our first release since we announced our new approach to supporting new compilers in this thread. All support for compilers versions >= 5.3 is implemented using this technique and new language features are encoded into the AST. We've added Ast_builder and Ast_pattern functions to allow you to manipulate some of those, such as labeled tuples or effect patterns. You can see those in our API documentation here and there. We've also illustrated how to use them in our new manual section. If you're interested in producing or consuming other new language features that cannot be represented with our current internal AST (5.2), please open an issue so we can add the relevant helpers.

Given the ecosystem hasn't yet recovered from the 5.2 AST bump and ppxlib.0.36.0, we're glad that we can add support for new compilers without introducing further breakage and keep the maintenance burden within ppxlib's bounds. We've started discussions with the compiler team to make this approach even more viable in the future on our end.

We'd like to thank @ceastlund who's our only external contributor for this release.

I'd personally like to thank @patricoferris for his help getting this out the door as well as the OCaml Software Foundation and OCamlPro for funding my work on ppxlib.

Thank you for reading and happy preprocessing!

You can comment on this announcement on the OCaml discuss forums.

Dune 3.22.0

2026-03-19T00:00:00-00:00

The Dune team is pleased to announce the release of dune 3.22.0.

In addition to many fixes and small improvements, notable highlights of this release include:

Fixes to the dune cache on Windows, thanks to @Nevor in ocaml/dune#13713.
New tracing functionality, to inspect and diagnose the build processes thanks to @rgrinberg across many PRs. See the documentation.
Addition of the dune-action-trace library, to instrument trace emission, thanks to @rgrinberg.
Support for generating odoc documentation in markdown via the @doc-markdown build alias thanks to @davesnx ocaml/dune#12581.
Full support for OxCaml's parameterised libraries, thanks to @art-w and @maiste. To learn more, see the docs.

See the full changelog for all new features and fixes, and for attribution to the contributors who made it all possible. Thank you, contributors!

If you encounter a problem with this release, please report it in our issue tracker.

You can comment on this announcement on the OCaml discuss forums.

OCamlFormat 0.29.0

2026-03-17T00:00:00-00:00

CHANGES:

Highlight

* Support OCaml 5.5 syntax
(#2772, #2774, #2775, #2777, #2780, #2781, #2782, #2783, @Julow)
The update brings several tiny changes, they are listed below.
* Update Odoc's parser to 3.0 (#2757, @Julow)
The indentation of code-blocks containing OCaml code is reduced by 2 to avoid
changing the generated documentation. The indentation within code-blocks is
now significative in Odoc and shows up in generated documentation.

Added

Added option letop-punning (#2746, @WardBrian) to control whether
punning is used in extended binding operators.
For example, the code let+ x = x in ... can be formatted as
let+ x in ... when letop-punning=always. With letop-punning=never, it
becomes let+ x = x in .... The default is preserve, which will
only use punning when it exists in the source.
This also applies to let%ext bindings (#2747, @WardBrian).

Support the unnamed functor parameters syntax in module types
(#2755, #2759, @Julow)

module type F = ARG -> S

The following lines are now formatted as they are in the source file:

module M : (_ : S) -> (_ : S) -> S = N
module M : S -> S -> S = N
(* The preceding two lines are no longer turned into this: *)
module M : (_ : S) (_ : S) -> S = N

Fixed

Fix dropped comment in (function _ -> x (* cmt *)) (#2739, @Julow)

* cases-matching-exp-indent=compact does not impact begin end nodes that
don't have a match inside. (#2742, @EmileTrotignon)

(* before *)
begin match () with
| () -> begin
  f x
end
end
(* after *)
begin match () with
| () -> begin
    f x
  end
end

Ast_mapper now iterates on all locations inside of Longident.t,
instead of only some.
(#2737, @v-gb)
Remove line break in M with module N = N (* cmt *) (#2779, @Julow)

Internal

Added information on writing tests to CONTRIBUTING.md (#2838, @WardBrian)

Changed

indentation of the end keyword in a match-case is now always at least 2. (#2742, @EmileTrotignon)

(* before *)
begin match () with
| () -> begin
  match () with
  | () -> ()
end
end
(* after *)
begin match () with
| () -> begin
  match () with
  | () -> ()

* use shortcut begin end in match cases and if then else body. (#2744, @EmileTrotignon)

(* before *)
match () with
| () -> begin
    match () with
    | () ->
  end
end
(* after *)
match () with
| () ->
  begin match () with
    | () ->
  end
end

* Set the ocaml-version to 5.4 by default (#2750, @EmileTrotignon)
The main difference is that the effect keyword is recognized without having
to add ocaml-version=5.3 to the configuration.
In exchange, code that use effect as an identifier must use
ocaml-version=5.2.
The work to support OCaml 5.5 come with several improvements:
- Improve the indentation of let structure-item with the
  [@ocamlformat "disable"] attribute.
  let structure-item means let module, let open, let include and
  let exception.
- (let open M in e)[@a] is turned into let[@a] open M in e.
- Long let open ... in no longer exceed the margin.
- Improve indentation of let structure-item within parentheses:
```
(* before *)
(let module M = M in
M.foo)
(* after *)
(let module M = M in
 M.foo)
```

Opam-publish 3.0.0

2026-02-20T00:00:00-00:00

CHANGES:

No longer allow option names to be specified by a prefix if the prefix is unambiguous [#202 @kit-ty-kate]
Query upstream repo for default branch instead of defaulting to master [#201 @mbarbin]
Query fork name from GitHub to support users whose fork of opam-repository isn't named opam-repository [#199 @mbarbin]
Fix an infinit loop if the user repeatedly provided an invalid token [#186 @filipeom]
Remove the deprecated --split option [#194 @kit-ty-kate]
Remove the github-unix dependency [#196 @kit-ty-kate]
Upgrade to cmdliner 2.0 [#202 @kit-ty-kate]

Release of OCaml 5.4.1 and 4.14.3

2026-02-17T00:00:00-00:00

We have the pleasure of announcing the dual releases of OCaml 4.14.3 and OCaml 5.4.1, dedicated to the memory of Nicolaas Govert de Bruijn on the anniversary of his death.

Those releases are a collection of safe and valuable runtime bugfixes. The OCaml 5.4.1 release also contains a fix for the -pack mode for macOs and various TSAN fixes.

More importantly, those new versions harden the Marshal module against malicious inputs as described in the security announcement OSEC-2026-01.

We are encouraging you to switch to those new releases whenever possible.

Don't hesitate to report any bugs on the OCaml issue tracker and to leave comments on the discuss announcement.

See the list of changes below for more details.

Happy hacking, -- Florian Angeletti for the OCaml team.

Installation Instructions

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

opam update
opam switch create 4.14.3
opam switch create 5.4.1

The source code for the release is also directly available on: