Section 5 of the EUPL contains the Compatibility Clause, which allows the distribution of derivative works under a compatible license.
The clause reads as follows:
"If the Licensee Distributes or Communicates Derivative Works or copies thereof based upon both the Work and another work licensed under a Compatible Licence, this Distribution or Communication can be done under the terms of this Compatible Licence. For the sake of this clause, ‘Compatible Licence’ refers to the licences listed in the appendix attached to this Licence. Should the Licensee's obligations under the Compatible Licence conflict with his/her obligations under this Licence, the obligations of the Compatible Licence shall prevail."
Some have questioned (in various external discussions) whether distribution under a compatible license offers a way to circumvent the coverage of remote interaction or SaaS, in particular when distributing under the GPL. The EUPL FAQs argue that there is no conflict because none of the compatible licenses prohibits this coverage. It is therefore maintained. However, GPL #7 invalidates "further restrictions." Yes, but the same GPL #13 allows relicensing under the AGPL, which indicates that SaaS coverage is not seen by the GPL as a restriction, but rather as an option for granting enhanced protection. To clarify this point, a more explicit formulation of the compatibility clause is being considered, as follows:
Licensees may Distribute or Communicate under the terms of a ‘Compatible Licence’ (listed in the appendix attached to this Licence) Derivative Works or copies thereof based upon both the Work and another work already licensed under the Compatible Licence, in so far these terms impose to do so. Should the Licensee's obligations under the Compatible Licence conflict with obligations under this Licence, the obligations of the compatible licence shall prevail, provided that the rights granted by this Licence and its definition of ‘Distribution or Communication to the public’, are applied.[CM1]
[CM1]The goal of this rewriting is not a change, but to remain that changing the licence of a derivative is only allowed when the compatible licence impose to do so, and that the SaaS coverage must persist (this is already the constant opinion expressed in the EUPL FAQs).
We (the EC as the EUPL licence steward) cannot assume that all other licence stewards (in particular FSF regarding GPL-3.0) will consider/accept this specific condition: it would be up to them to say so to their own users, as the case may be (if they disagree they could not benefit from compatibility, or ensure it by linking only, which, when implemented between independent software components, is not producing a derivative according to the European law).
It could be added (but perhaps it is not necessary, because already evident) that: "This clause applies to the specific Derivative Work only and may not be used for the purpose of relicensing the Original Work."
Comments on this proposal are welcome. The new formulation is not seen as a change, but as a clarification. This may lead to the publication (probably in early 2027) of the EUPL-1.3
Comments
Initiated 6 months ago at the end of 2025, this discussion on "Hackers News" illustrates the complexity of compatibility, and maybe the necessity of bringing some clarification in the EUPL compatibility clause.