A New Frontier for Added Subject-Matter at the EPO?

At the European Patent Office (EPO), a recent referral of case T 873/24 from the Technical Board to the Enlarged Board of Appeal may clarify whether last summer’s decision in case G 1/24 on claim interpretation may be extended to the analysis of Added Subject-Matter. Already G 1/24 is impacting the assessment of patentability at the EPO, but should this referral be allowed, G 1/24’s effect on the assessment of added matter could result in a real shake up of the EPO’s notoriously strict assessment of support. Nonetheless, a review of how we got here highlights the value of late arguments during the EPO appeal process.

Background

Last summer the EPO’s most senior board (the Enlarged Board of Appeal) heard case G 1/24 regarding a vaping technology, where patentability hinged on how the claims were interpreted. In opposition proceedings, the Patentee had successfully argued that the claim term “gathered sheet” was a term of art, such that the claims could be interpreted without reference to the description.

However, on appeal, the Enlarged Board was asked to consider a fundamental legal principle: Is it possible to use a straightforward interpretation of the claim per se based on standard terms of art in the field, in a case where a non-standard definition for a claim term is explicitly provided in the accompanying description?

The Enlarged Board concluded that this is not possible and set out, inter alia, the following principles:

• “The description and any drawings are always referred to when interpreting the claims, and not just in the case of unclarity or ambiguity.”
• “The finding that the language of a claim is clear and unambiguous is an act of interpretation, not a preliminary stage to such an interpretative act.”

G 1/24 applied the above principles when discussing patentability. However, it has subsequently been argued that these principles should be applied in other situations requiring claim interpretation.

Recent Developments

Granted patent EP3587104 (“Coated steel strips,” T 873/24) was opposed on patentability and added subject-matter grounds. The Opponent succeeded at first instance with some of their patentability arguments, but the patent was maintained in an amended form.

The Opponent appealed, continuing their argument that the amended form of the patent includes added subject-matter and should not have been maintained at all. The above decision on case G 1/24 was issued in June 2025, while the Steel Strips appeal was pending. The G 1/24 decision was subsequently introduced to this appeal by the Opponent to reinforce some clarity arguments. However, the preliminary opinion of the Technical Board of Appeal (TBA) in October 2025 did not contain any hint of the possibility of another referral to the Enlarged Board. Indeed, in the preliminary opinion, the TBA appeared ready to revoke the patent without specific discussion of the new case law.

In fact, it was only a few weeks prior to the TBA hearing, when the Proprietor suggested that G 1/24 might be relevant for assessing added subject-matter. Claim 1 recites a ratio of constituents, and the Proprietor argued that this ratio should be interpreted as a ratio of weight% values of the constituents. The Proprietor noted that this interpretation would be consistent with the detailed description and argued that the principles of G 1/24 require such an interpretation to be adopted. Typically, late submissions are frowned upon at the EPO’s Boards of Appeal. However, in this instance it appears that the Proprietor was able to successfully obtain a referral to the higher board, based on a line of argument introduced in the late submission.

At a hearing lasting just over an hour (which is extremely brief by typical Opposition/Appeal standards), a complete conclusion to the case was postponed, as the parties consented to refer important questions of law to the Enlarged Board of Appeal:

• Should any of the principles of decision G 1/24 be applied when assessing added subject-matter?
• If so, to what extent?

Detailed questions for the Enlarged Board will be set out in due course.

Practice Notes

• It is never too late to try an argument. The EPO’s procedural rules for efficient handling of cases can be quite stringent, but this case demonstrates that a substantive argument can sometimes win out over procedural considerations.
• If G 1/24 is applied to added subject-matter, this may be a good or bad thing for the patentee in different circumstances. For example, as the Proprietor argues in this case, an interpretation based on the description may remove an apparent discrepancy between a claim and a described embodiment. On the other hand, in some circumstances, an interpretation based on the description could be used to argue that an amended claim recites an added combination of features beyond the original disclosure.
• In the written submission of August 2025 for Steel Strips, the Opponent also applied G 1/24 when making a clarity argument. It remains to be seen whether the Enlarged Board referral will solely be asked to consider added matter practice, or whether the Enlarged Board will also be asked to consider the extent to which G 1/24 applies to clarity.
• If G 1/24 is applied to clarity, this may again be good or bad for the patentee in different circumstances. Interpreting a claim in light of the description may help to resolve some clarity objections. On the other hand, a reference to the description may be used to highlight a risk of confusion between the claim scope as it initially appears, and the claim scope as properly interpreted in light of the description.
• G 1/24 already highlighted the practice point that “The correct response to any unclarity in a claim is amendment.” This already indicates that G 1/24 may potentially be used by examiners as a reason to avoid backing down when a clarity objection has been raised.