# Announcement of 4.2.1 Bugfix Release

**URL:** <https://nemo-ocean.discourse.group/t/announcement-of-4-2-1-bugfix-release/537>\
**Category:** Annoucements\
**Created:** [21 July 2023 07:53 UTC](https://nemo-ocean.discourse.group/t/announcement-of-4-2-1-bugfix-release/537 "2023-07-21T07:53:29Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Kat\_Hutchinson](https://avatars.discourse-cdn.com/v4/letter/k/e95f7d/32.png) [@Kat\_Hutchinson](https://nemo-ocean.discourse.group/u/Kat_Hutchinson)\
**Post date:** [21 July 2023 07:53 UTC](https://nemo-ocean.discourse.group/t/announcement-of-4-2-1-bugfix-release/537/1 "2023-07-21T07:53:30Z")

</div>

**NEMO v4.2.1 is now available!**

**To checkout the 4.2.1 release** :

```console
git clone --branch 4.2.1 https://forge.nemo-ocean.eu/nemo/nemo.git nemo_4.2.1

```

**Full list of changes since 4.2.0** available [here](https://sites.nemo-ocean.io/user-guide/changes.html)

**Migration guide from 4.0 to 4.2** available [here](https://sites.nemo-ocean.io/user-guide/migration.html)

**Brief summary of highlights:**

NEMO version 4.2.1 can be viewed largely as a bugfix release with very minor highlights in terms of developments. For details on all changes since the 4.2.0, please refer to [this](https://sites.nemo-ocean.io/user-guide/changes.html) page. Notably, small improvements to the NEMO-TOP interface were made, especially the robustness of passive tracer conservation for the euler-forward time-stepping scheme. An issue with the option ln\_top\_euler = .true. has been resolved as implementation of this was found to possibly result in small drifts in passive tracer inventories. Furthermore, a restartability issue affecting some configurations with euler-forward time-stepping of passive tracers has been addressed, along with improvements in offline transport when using the linear free surface option. Conservation of passive tracers is now restored to the level of uncertainty expected from double precision arithmetic. Debugging of HPC capabilities now means that the model can be run in single precision to save cpu time (using the cpp key key\_single). Note that the results are not as accurate as when running in double precision. Additionally, demonstration of mixed-precision compilation for ORCA2 is available with further details [here](https://sites.nemo-ocean.io/user-guide/mixed.html). It is now possible to use the new version of the input/output manager, XIOS3, instead of XIOS2 with the cpp key “key\_xios3” (which needs to be added alongside “key\_xios”), see user guide [section](https://sites.nemo-ocean.io/user-guide/install.html#install-xios-library) for further instructions. Finally, it is important to note that tiling capabilities are not fully functional in the 4.2.1 and so we do not recommend the activation of this option.

The Nemo System Team strongly encourages users working with version 4.2.0 to upgrade to this new bugfix release. For new users, please refer to [this](https://sites.nemo-ocean.io/user-guide/install.html#download-and-install-the-nemo-code) page for instructions on installation.

**Documentation:**

- NEMO Ocean Engine [Reference Manual](https://doi.org/10.5281/zenodo.8167700)

- NEMO Sea Ice Engine [Reference Manual](https://doi.org/10.5281/zenodo.7534900)

- NEMO Tracers Engine [Reference Manual](https://doi.org/10.5281/zenodo.1471700)