# OCaml 5.4.0 — OCaml 5.4.0

- Product: OCaml (https://whatsnew.fyi/product/ocaml)
- Vendor: OCaml
- Date: 2025-10-09
- Version: 5.4.0
- Original notes: https://github.com/ocaml/ocaml/releases/tag/5.4.0
- Permalink: https://whatsnew.fyi/product/ocaml/releases/5.4.0

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **added** — Labelled tuples
- **added** — Immutable arrays
- **added** — Array literal syntax support for immutable arrays and floatarrays through type-directed disambiguation
- **added** — Atomic record fields
- **added** — Four new standard library modules: Pair, Pqueue, Repr, and Iarray
- **added** — More than thirty new standard library functions
- **added** — New chapter in the manual on profiling OCaml programs on Linux and macOS
- **changed** — Restored memory cleanup upon exit mode
- **changed** — Many runtime and code generation improvements
- **changed** — Nearly a dozen improved error messages
- **fixed** — Around fifty bug fixes

Some of the highlights of OCaml 5.4.0 are:

- Labelled tuples
- Immutable arrays
- Array literal syntax support for immutable arrays and `floatarray`s
  (through type-directed disambiguation)
- Atomic record fields
- Four new standard library modules: Pair, Pqueue, Repr, and Iarray
- Restored "memory cleanup upon exit" mode
- New chapter in the manual on profiling OCaml programs on Linux and macOS

And a lot of incremental changes:

- Many runtime and code generation improvements
- More than thirty new standard library functions
- Nearly a dozen improved error messages
- Around fifty bug fixes