# Release 2.31.0 (2025-08-21)

- `build-cores = 0` now auto-detects CPU cores [#13402](https://github.com/NixOS/nix/pull/13402)

  When `build-cores` is set to `0`, Nix now automatically detects the number of available CPU cores and passes this value via `NIX_BUILD_CORES`, instead of passing `0` directly. This matches the behavior when `build-cores` is unset. This prevents the builder from having to detect the number of cores.

- Fix Git LFS SSH issues [#13337](https://github.com/NixOS/nix/issues/13337) [#13743](https://github.com/NixOS/nix/pull/13743)

  Fixed some outstanding issues with Git LFS and SSH.

  * Added support for `NIX_SSHOPTS`.
  * Properly use the parsed port from URL.
  * Better use of the response of `git-lfs-authenticate` to determine API endpoint when the API is not exposed on port 443.

- Add support for `user@address:port` syntax in store URIs [#7044](https://github.com/NixOS/nix/issues/7044) [#3425](https://github.com/NixOS/nix/pull/3425)

  It's now possible to specify the port used for SSH stores directly in the store URL in accordance with [RFC3986](https://datatracker.ietf.org/doc/html/rfc3986). Previously the only way to specify custom ports was via `ssh_config` or the `NIX_SSHOPTS` environment variable, because Nix incorrectly passed the port number together with the host name to the SSH executable.

  This change affects [store references](@docroot@/store/types/index.md#store-url-format) passed via the `--store` and similar flags in CLI as well as in the configuration for [remote builders](@docroot@/command-ref/conf-file.md#conf-builders). For example, the following store URIs now work:

  - `ssh://127.0.0.1:2222`
  - `ssh://[b573:6a48:e224:840b:6007:6275:f8f7:ebf3]:22`
  - `ssh-ng://[b573:6a48:e224:840b:6007:6275:f8f7:ebf3]:22`

- Represent IPv6 RFC4007 ZoneId literals in conformance with RFC6874 [#13445](https://github.com/NixOS/nix/pull/13445)

  Prior versions of Nix since [#4646](https://github.com/NixOS/nix/pull/4646) accepted [IPv6 scoped addresses](https://datatracker.ietf.org/doc/html/rfc4007) in URIs like [store references](@docroot@/store/types/index.md#store-url-format) in the textual representation with a literal percent character: `[fe80::1%18]`. This was ambiguous, because the the percent literal `%` is reserved by [RFC3986](https://datatracker.ietf.org/doc/html/rfc3986), since it's used to indicate percent encoding. Nix now requires that the percent `%` symbol is percent-encoded as `%25`. This implements [RFC6874](https://datatracker.ietf.org/doc/html/rfc6874), which defines the representation of zone identifiers in URIs. The example from above now has to be specified as `[fe80::1%2518]`.


## Contributors


This release was made possible by the following 34 contributors:

- John Soo [**(@jsoo1)**](https://github.com/jsoo1)
- Alan Urmancheev [**(@alurm)**](https://github.com/alurm)
- Manse [**(@PedroManse)**](https://github.com/PedroManse)
- Pol Dellaiera [**(@drupol)**](https://github.com/drupol)
- DavHau [**(@DavHau)**](https://github.com/DavHau)
- Leandro Emmanuel Reina Kiperman [**(@kip93)**](https://github.com/kip93)
- h0nIg [**(@h0nIg)**](https://github.com/h0nIg)
- Philip Taron [**(@philiptaron)**](https://github.com/philiptaron)
- Eelco Dolstra [**(@edolstra)**](https://github.com/edolstra)
- Connor Baker [**(@ConnorBaker)**](https://github.com/ConnorBaker)
- kenji [**(@a-kenji)**](https://github.com/a-kenji)
- Oleksandr Knyshuk [**(@k1gen)**](https://github.com/k1gen)
- Maciej Krüger [**(@mkg20001)**](https://github.com/mkg20001)
- Justin Bailey [**(@jgbailey-well)**](https://github.com/jgbailey-well)
- Emily [**(@emilazy)**](https://github.com/emilazy)
- Volker Diels-Grabsch [**(@vog)**](https://github.com/vog)
- gustavderdrache [**(@gustavderdrache)**](https://github.com/gustavderdrache)
- Elliot Cameron [**(@de11n)**](https://github.com/de11n)
- Alexander V. Nikolaev [**(@avnik)**](https://github.com/avnik)
- tomberek [**(@tomberek)**](https://github.com/tomberek)
- Matthew Kenigsberg [**(@mkenigs)**](https://github.com/mkenigs)
- Sergei Zimmerman [**(@xokdvium)**](https://github.com/xokdvium)
- Cosima Neidahl [**(@OPNA2608)**](https://github.com/OPNA2608)
- John Ericson [**(@Ericson2314)**](https://github.com/Ericson2314)
- m4dc4p [**(@m4dc4p)**](https://github.com/m4dc4p)
- Graham Christensen [**(@grahamc)**](https://github.com/grahamc)
- Jason Yundt [**(@Jayman2000)**](https://github.com/Jayman2000)
- Jens Petersen [**(@juhp)**](https://github.com/juhp)
- the-sun-will-rise-tomorrow [**(@the-sun-will-rise-tomorrow)**](https://github.com/the-sun-will-rise-tomorrow)
- Farid Zakaria [**(@fzakaria)**](https://github.com/fzakaria)
- AGawas [**(@aln730)**](https://github.com/aln730)
- Robert Hensing [**(@roberth)**](https://github.com/roberth)
- Dmitry Bogatov [**(@KAction)**](https://github.com/KAction)
- Jörg Thalheim [**(@Mic92)**](https://github.com/Mic92)
- Philipp Otterbein