CUPS is developed by Apple Inc. and distributed as open source software under the Apache License, Version 2.0. Significant contributions to CUPS must be licensed to Apple using the Apple Contributor Agreement:
https://www.cups.org/AppleContributorAgreement_2011-03-10.pdf
Contributions should be submitted as attachments to bug reports on the CUPS web site. Changes to existing source files should be submitted as unified diffs (both Subversion and Git produce this format by default) while new source files should be provided as-is or in an archive. Github pull requests can also be used to submit changes.