Athena Releases

Last update: 14 Dec 2022 [History] [Edit]

Release Numbers

When a particular build of an Athena project is deemed ready for production it will be installed as a numbered release onto the ATLAS production CVMFS server.

ATLAS software is numbered according to the following scheme:


A refers to the release series, e.g., release series 23 is used for Run 3 simulation and data taking 2023. NB that the release series matching the data taking year is here coincidental, and does not represent a convention.

B is the release flavour and usually corresponds to a particular branch in the git repository for which the code base needs to be different. e.g., 23.0 is the release series for MC23 simulation, and 2023 Tier-0 reconstruction & Trigger, while 23.2 is the release series for analysis.

Principle release flavours are:

Flavour Purpose
0 Tier-0 reconstruction, trigger, and corresponding simulation production
2 Derivations and Analysis
6 Event Generation

The numbering scheme reflects historical releases where a larger number of different flavours were created. These have been consolidated since release 22.0 resulting in fewer projects, but the numbering for those that remain was kept the same to remain consistent.

Note that while there is a strong correspondence between release flavour and Athena Project, it is not absolute: e.g., AthDerivation and AthAnalysisBase would both be built from flavour 2.

X is the major release number, monotonically increasing as code is developed with bugs fixed and enhancements added.

Occasionally, Y will be used is a minor release number is required for developments that branched from an older major release. e.g., 21.0.20.Y contained any fixes required for MC16a, as releases 21.0.21 onwards contained incompatible changes for MC16c. Most releases will not have a minor release number, and so A.B.X is fully sufficient.

Setting Up A Release

To setup a production release the release number and project need to be specified to asetup, e.g.,

asetup Athena,23.0.11

Release History


Release 23.0 is the current release for 2023 data taking, trigger, reprocessing, and MC production. It is a largely technical update with respect to 22.0, in order to provide a stable release through to the end of Run3, and provides full backwards-compatibility with outputs produced in that release. Switching between 22.0 and 23.0 should therefore require only minor adaptations if any.

Some key features are:

  • Use of HEPMC3 and 64-bit event numbers, allowing for compatibility with future generator versions and larger event generation files to be produced, respectively.
  • Updated the LCG version (LCG_102b) used for providing common libraries such as ROOT, allowing for future compatibility with Centos9s/AlmaLinux9/RHEL9 operating systems.
  • Extensive availability of ComponentAccumulator-based job configuration.

AOD files produced in 23.0 can be used to produce derivations in 24.0-series releases (see the description in earlier section)


Release 22.0 was the release used for initial Run3 data taking, trigger, reprocessing, and MC production in 2022. It represents the culmination of a multi-year development program:

  • It was the first Athena release to fully support AthenaMT for multi-threaded event processing
  • It also features numerous other improvements to reconstruction, including significant speed-ups of Inner Detector tracking allowing inclusion of dedicated tracking for long-lived particles as part of the standard chain
  • It includes reconstruction and simulation of the Muon New Small Wheel
  • Additionally, it is the first release series where Run4 detectors can be simulated and reconstructed in the same release as the current detectors.

AOD files produced in 22.0 can be used to produce derivations in 23.0-series releases (up to 23.0.11)


Release 21.0 was the release for Run2 data taking, trigger, reprocessing, and MC production. It was the release series in which the current CMake-based build system, and gitlab-based code versioning, were first used.

NB future reprocessings of Run2 data, and associated MC productions, will be performed in 23.0 (or newer)

Releases prior to 21.0 used an entirely different release building and versioning infrastructure, and so are not covered here.

Finding Releases and Release Information

It is very easy to see which production releases are available, just by looking in CVMFS, e.g.,

$ ls /cvmfs/
23.0.0  23.0.1  23.0.10  23.0.11  23.0.2  23.0.3  23.0.4  23.0.5  23.0.6  23.0.7  23.0.8  23.0.9

Where the release series and flavour are encoded in the highest level directory, then the project, then the release number (/cvmfs/

See the full asetup users guide for further options.

Release Notes

When a git tag is made for a production release the release coordinator will add some release notes to the tag, which you can read directly in GitLab (just navigate to the tag of interest) or through the git command line:

$ git show release/23.0.11
tag release/23.0.11
Tagger: Tadej Novak <>
Date:   Wed Dec 7 13:27:09 2022 +0100

Release for derivations production and physics validation
commit 115629ba8b6a28ad16c5c09dff994a3c43339faf (tag: release/23.0.11, tag: release/22.6.26, tag: nightly/master/2022-12-07T0501, tag: nightly/master/2022-12-07T0313, tag: nightly/master/2022-12-07T0220, tag: nightly/master/2022-12-07T0001, tag: nightly/master/2022-12-06T2300, tag: nightly/master/2022-12-06T2101, tag: nightly/master/2022-12-06T2001, tag: nightly/master/2022-12-06T2000)
Merge: e823350ccd3 7681d5affec

Mapping Releases to Nightly Builds

If you need to find out which nightly build corresponded to a particular release the ReleaseData file contains useful information:

$ cat /cvmfs/ 
nightly name:master
project name:Athena
nightly release:115629ba8b6

You can also search for references with the right tag or hash in git using git describe:

$ git describe --tags --match 'release/*' nightly/22.0/2022-11-01T2101

$ git describe --tags --match 'nightly/*' release/22.0.101            

$ git describe --tags --match 'nightly/*' 5a344df38c0