# First release candidate for OCaml 5.5.0 **URL:** \ **Category:** Ecosystem\ **Created:** [June 11, 2026, 1:41pm UTC](https://discuss.ocaml.org/t/first-release-candidate-for-ocaml-5-5-0/18253 "2026-06-11T13:41:55Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![octachron](https://avatars.discourse-cdn.com/v4/letter/o/49beb7/32.png) [@octachron](https://discuss.ocaml.org/u/octachron)\ **Post date:** [June 11, 2026, 1:41pm UTC](https://discuss.ocaml.org/t/first-release-candidate-for-ocaml-5-5-0/18253/1 "2026-06-11T13:41:55Z")
The release of OCaml 5.5.0 is imminent. As a final step, we are publishing a release candidate to check that everything is in order before the release in the upcoming week. If you find any bugs, please report them on the [OCaml’s issue tracker](https://github.com/ocaml/ocaml/issues). Compared to the first beta, this release candidate contains two runtime fixes, two standard library fixes, six miscellaneous fixes and one documentation update. The full change log for OCaml 5.5.0 is [available on GitHub](https://github.com/ocaml/ocaml/blob/5.5/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 and later: ``` opam update opam switch create 5.5.0~rc1 ``` The source code for the release candidate is also directly available on: - GitHub: [https://github.com/ocaml/ocaml/archive/5.5.0-rc1.tar.gz](https://github.com/ocaml/ocaml/archive/5.5.0-rc1.tar.gz) - OCaml archives at Inria: [https://caml.inria.fr/pub/distrib/ocaml-5.5/ocaml-5.5.0~rc1.tar.gz](https://caml.inria.fr/pub/distrib/ocaml-5.5/ocaml-5.5.0~rc1.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 ocaml-variants.5.5.0~rc1+options ``` where `` is a space-separated list of `ocaml-option-*` packages. For instance, for a `flambda` and `no-flat-float-array` switch: ``` opam switch create 5.5.0~rc1+flambda+nffa ocaml-variants.5.5.0~rc1+options ocaml-option-flambda ocaml-option-no-flat-float-array ``` All available options can be listed with `opam search ocaml-option`. * * * ## Changes since the first beta release ### Runtime fixes - [#14820](https://github.com/ocaml/ocaml/issues/14820): caml\_ba\_alloc must account for memory it allocated itself. CAML\_BA\_SUBARRAY (introduced in 5.2) with data=NULL would result in the Gc accounting for the allocation as 0 bytes, which can eventually lead to OOM. This condition never occurs in the compiler itself, but occurs in external C bindings that attempt to create a new bigarray in the shape of an existing one. For backwards compatibility ignore CAML\_BA\_SUBARRAY when data is NULL. (Edwin Török, review by Damien Doligez) - …, +[#14722](https://github.com/ocaml/ocaml/issues/14722): runtime, fix in the orphaning of ephemerons (Gabriel Scherer, review by Olivier Nicole and Damien Doligez, report by Jan Midtgaard) ### Standard library fix - [#14853](https://github.com/ocaml/ocaml/issues/14853), CVE-2026-41083, OSEC-2026-05: fix quoting of filenames passed to `Filename.quote_command` on Windows. (David Allsopp, report by Andrew Nesbitt, review by Florian Angeletti) - …, +[#14715](https://github.com/ocaml/ocaml/issues/14715): Use POSIX thread-safe getgrnam\_r, getgrgid\_r, getpwnam\_r, getpwuid\_r, gmtime\_r, localtime\_r, getlogin\_r, and fix mktime error checking. (Antonin Décimo, review by Florian Angeletti, David Allsopp, Stefan Muenzel, Gabriel Scherer, and Miod Vallat) ### Compiler user-interface fix - [#14702](https://github.com/ocaml/ocaml/issues/14702): Fix hidden directory files leaking into the visible load path table. When a hidden directory contained a file whose basename was already present, the file could be incorrectly added to the visible table. (Hugo Heuzard, review by Florian Angeletti) ### Compilerlibs fix - [#14797](https://github.com/ocaml/ocaml/issues/14797): avoid dropping attributes attached to package types when pretty printing in surface syntax. (Chet Murthy, review by Nicolás Ojeda Bär) ### Configuration fixes - [#14484](https://github.com/ocaml/ocaml/issues/14484): Set `_WIN32_WINNT` to require Windows 8/Server 2012 Windows header SDK support. (Antonin Décimo, review by David Allsopp) - [#14760](https://github.com/ocaml/ocaml/issues/14760), [#14802](https://github.com/ocaml/ocaml/issues/14802), [#14846](https://github.com/ocaml/ocaml/issues/14846): Correct the detection of argument defaults in configure, fixing an incorrect error message when installing OCaml through opam on OpenSUSE with the site-config package installed. (David Allsopp, report and review by Edwin Török) ### Documentation fix - [#14684](https://github.com/ocaml/ocaml/issues/14684), [#14782](https://github.com/ocaml/ocaml/issues/14782), [#14838](https://github.com/ocaml/ocaml/issues/14838): Improve ocamlc’s and ocamlopt’s manual pages and fix small issues in the manual (Samuel Hym, review by Florian Angeletti, Antonin Décimo, Gabriel Scherer and Nicolás Ojeda Bär) ### Internal fix - …, +[#14550](https://github.com/ocaml/ocaml/issues/14550): Add the not-root builtin ocamltest action. This allows to skip tests that fail if the current user is root (superuser). (Kate Deplaix, review by Gabriel Scherer, Nicolás Ojeda Bär, and Antonin Décimo) ---
**Author:** ![octachron](https://avatars.discourse-cdn.com/v4/letter/o/49beb7/32.png) [@octachron](https://discuss.ocaml.org/u/octachron)\ **Post date:** [June 11, 2026, 1:50pm UTC](https://discuss.ocaml.org/t/first-release-candidate-for-ocaml-5-5-0/18253/2 "2026-06-11T13:50:30Z")
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**Author:** ![mneumann](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/mneumann/32/6522_2.png) [@mneumann](https://discuss.ocaml.org/u/mneumann)\ **Post date:** [June 11, 2026, 7:54pm UTC](https://discuss.ocaml.org/t/first-release-candidate-for-ocaml-5-5-0/18253/3 "2026-06-11T19:54:40Z")
There’s a `TODO: ` that probably needs to be removed [ocaml/Changes at 5.5 · ocaml/ocaml · GitHub](https://github.com/ocaml/ocaml/blob/5.5/Changes#L165)