Geant4 license clarification or standardization

ferhue · July 21, 2026, 8:13am

The fact that the Geant4 collaboration chose not to use any of the over 300 standard licenses ( SPDX License List | Software Package Data Exchange (SPDX)) and created yet-another-custom-one is leading to quite some issues and lengthy legal-team discussions, including the removal of Geant4 (geant4 10.7.0 by drbenmorgan · Pull Request #66422 · Homebrew/homebrew-core · GitHub) from Homebrew-core package manager (geant4: delete by Bo98 · Pull Request #72029 · Homebrew/homebrew-core · GitHub, formula by @bmorgan), and its non-compliance with GPL and DFSG (I Challenge Thee), leading to be considered non-free software inside Debian repositories.

Being used by such a huge number of users and physicists, I would like to kindly ask the team / developers to:

Answer to the thread by @stephanlachnit: I Challenge Thee regarding DFSG compliance since it is subject to interpretation.
Answer / chime in to New license request: G4SL · Issue #3038 · spdx/license-list-XML · GitHub
In future Geant4 (v12?) releases, move towards more standard licenses rather than custom ones, following that the ROOT team at CERN has done recently by reviewing GPL dependencies, etc. Stanford did the same, switching to BSD3: General Software License (2007-)
Or otherwise ensure it appears on SPDX if none of the >300 matches what Geant4 requires.

Thanks a lot in advance!

PS:
Local homebrew taps as workaround:

github.com/brewsci/homebrew-science

Formula/geant4.rb

master

class Geant4 < Formula
  desc "Simulation toolkit for particle transport through matter"
  homepage "http://geant4.cern.ch"
  url "http://geant4.cern.ch/support/source/geant4.10.03.p03.tar.gz"
  version "10.3.3"
  sha256 "a164f49c038859ab675eec474d08c9d02be8c4be9c0c2d3aa8e69adf89e1e138"

  bottle do
    root_url "https://archive.org/download/brewsci/bottles-science"
    sha256 cellar: :any, high_sierra:  "c772638082c68d6610ee73325e4cea2559a000e0b0f954a55be26154019bf105"
    sha256 cellar: :any, sierra:       "ec5643125522f34ebfce1125a838c34519b9bf356c63870d5c6c328a64e63b63"
    sha256 cellar: :any, el_capitan:   "b9b5bafa9f756f11a2a5113b8f3e058af2f07c1c21010ca7fe0cf7271cdd4016"
    sha256 cellar: :any, x86_64_linux: "ab2c884c84ace2445f714ef1a23482c4d902b6cae3ff5cb63befe37601e5a41e"
  end

  option "with-g3tog4", "Use G3toG4 Library"
  option "with-gdml", "Use GDML"
  option "with-usolids", "Use USolids (experimental)"
  option "without-multithreaded", "Build without multithreading support"

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bmorgan · July 21, 2026, 10:30am

Ultimately, DFSG compliance is up to Debian Legal to decide - the Geant4 license is what it is in that context. I don’t know what we would or could add to the discussion there.

Re-licensing would be a huge legal undertaking given the history of the project and its copyright holders. Not saying it’s not possible, just that it’s a lot of work.

We’re of course happy if the license gets incorporated in SPDX - but again, I’m not sure what posting on that thread would achieve.

If the goal is a homebrew tap for Geant4, we’d of course welcome contributions and maintainers towards this. GitHub - drbenmorgan/homebrew-geant4: Test tap for Geant4 Homebrew packaging · GitHub was an attempt towards this, but time and other projects intervened.