ZUGFeRD-csharp is the open-source .NET library most teams use to create and read ZUGFeRD, Factur-X and XRechnung invoices (about 1.7 million NuGet downloads). Its maintainer has announced that maintenance ends on 30 November 2026 . Until then there are only selected bug fixes and security reviews. After that the NuGet packages are marked as legacy and the repository is archived. New features and new standard versions go only into a commercial successor.

Nothing breaks on 1 December: version 18.0.1 keeps working, and its Apache 2.0 licence stays. The risk is the next rule change. The rules for German and French e-invoices are updated several times a year. KoSIT's last XRechnung configuration came out on 31 August 2026, and the French reform's rules are still moving.…