What changed in Fermitools 2.5.3?

Updated

Fermitools 2.5.3, released July 31, 2026, is a maintenance update that fixes user-reported bugs, updates backend libraries, and patches two significant issues from version 2.5.2. If you use Fermipy or generate radial Gaussian or radial disk source maps, this update addresses problems that could affect your analysis.

Key changes in 2.5.3

Library and dependency updates

  • Xerces-C removed: The XML parsing interface Xerces-C has been removed and replaced with the header-only rapidXML interface.
  • Python version bump: The toolchain moved from Python 3.11 to Python 3.12.

Bug fixes

  • Radial source map generation: This release fixes a critical bug that prevented the accurate generation of radial Gaussian and radial disk source maps.
  • Fermipy performance issue: A performance problem affecting analysis with Fermipy, introduced in version 2.5.2, has been patched.
  • User-reported fixes: The update includes a number of bug fixes reported by users as well as by FSSC team members.

Who should upgrade

Situation Recommendation
You generate radial Gaussian or radial disk source maps Upgrade — the previous release could not produce accurate maps
You run Fermipy analyses Upgrade — 2.5.2 had a performance regression
You rely on Xerces-C XML parsing Check compatibility — the interface has been replaced with rapidXML
You are on Python 3.11 Note the move to Python 3.12 before upgrading
You have no issues with your current version The update is available; review the release notes for details relevant to your workflow

Where to find more detail

The announcement links to full release notes for a complete list of changes. The Fermi Portal also hosts related notices, including a June 5, 2026 data quality flag issue in LAT spacecraft files that may affect high time resolution analyses such as pulsar studies — if your work falls in that category, the FSSC recommends re-downloading spacecraft files and reanalyzing your data.