Background

The EPO is renowned for its stringent approach to basis for claim amendments with its “gold standard” test being what a skilled person would derive directly and unambiguously, using common general knowledge, and seen objectively and relative to the date of filing, from the description as a whole; such that after amendment the skilled person may not be presented with new technical information. This test necessarily requires consulting the description at some level.

In the now seminal decision G1/24, the Enlarged Board of Appeal held that: “The description and drawings shall always be consulted to interpret the claims when assessing the patentability of an invention under Articles 52 to 57 EPC…”.

There have been many decisions subsequent to G1/24 that provide some guidance on how the consultation of the description should be applied to claim interpretation.

In our related article “Claim interpretation: emerging trends on what ‘consulting the description/drawings’ in G1/24 may mean” we discuss a selection of the decisions in which Boards have held that consulting the description generally does not mean that a claim can be construed more narrowly than the literal wording of the claim, and in our connected article “G1/24 and claim interpretation: consulting the description/drawings may broaden a claim” we review several diverging decisions in which Boards have held that the description may be used to broaden the meaning of a claim beyond its literal reading. However, notably, G1/24 did not discuss how the description should be consulted in the context of added subject-matter. This is now considered in the recent referral.

T0873/24

G1/26 is a referral from T0873/24, an appeal concerning European patent EP3587104. The claims granted in EP3587104 relate to pre-coated steel strips wherein the base steel comprises various components by weight percent and the key issue concerns whether the omission of units from the feature “the ratio of titanium to nitrogen is in excess of 3.42” in claim 1 adds subject-matter.

The Opposition Division had maintained the patent in an amended form and held that, in view of the claims as a whole, the use of the unit “weight percentage” for the amounts of titanium and nitrogen when calculating the ratio was the only possible interpretation, and that this was confirmed by the description.

Unsurprisingly, the patentee maintained this position during the appeal, additionally arguing that the use of weight percentage was in accordance with standard practice. Conversely, the opponent argued that the ratio feature was not limited to a weight ratio but encompassed other options, such as molar ratio. This alternative interpretation is technically sensible. The Opponent further asserted that the standard practice of using weight percentages could not be relied upon to meet the requirements of direct and unambiguous disclosure.

In its interlocutory decision, the Board found that the case hinges on the extent to which information in the description may influence the interpretation of claim 1. In connection to this, the Board considered that there are three divergent approaches in the case law applying G1/24 as to how the description is to be consulted in the assessment of added subject-matter and that the approach taken would lead to different outcomes when applied to this case.

In the first line of case law, the description is consulted only to define the skilled person and establish common general knowledge. Under this approach, the board concluded that claim 1 would be deemed to add subject-matter as the skilled person would not be able to determine from the wording of the claim which kind of ratio is being referred to.

The second approach requires consulting the specification in order to exclude claim interpretations which are incompatible with the technical context provided by the specification such there is no broadening or narrowing of claims based on the description. Following this line of case law, the Board concluded that claim 1 would be deemed to add subject-matter because interpreting the open ratio as a weight ratio would be a restriction, since interpretating the open ratio as a molar ratio cannot be excluded as an interpretation that is incompatible with the general technical context provided by the specification.

The third line of case law requires a holistic approach, in which the claims and description are to be read as a whole (a unitary process) in order to derive the meaning a skilled person would attribute to terms used in the claim. This approach permits a broadening and/or narrowing of the claim interpretation in view of the specification and aligns with the approach adopted by the UPC. Under this approach, the Board concluded that claim 1 would be deemed not to add subject-matter because the ratio of titanium to nitrogen is only mentioned in the context of a weight ratio in the specification and, thus, when read in the context of the description claim 1 is to be interpreted more narrowly than the claim alone would suggest.

In view of this diverging case law, the Board referred three questions to the Enlarged Board of Appeal, with the first question relating to a procedural point concerning when a Board is permitted to make referrals.

Questions referred to the Enlarged Board of Appeal

1. May a decision be considered to be “required” for the purposes of Article 112(1) EPC, if the referring Board demonstrates that the point of law in question arises out of the context of the case pending before it and, in the circumstances of the proceedings, it is reasonable for the Board to examine it and decide on it next?

2.(a) Does the fact that the claims are the starting point and the basis for assessing the patentability of an invention generally preclude a feature which is only disclosed in the description or the drawings of a patent from being read into the meaning of a granted claim, in particular if this leads to a restrictive reading of terms used in the claim?

2.(b) If the answer to question 2.(a) is “no”, is claim interpretation the result of both reading the claims and consulting the description and drawings as a unitary process and does the claim being the starting point and the basis for assessing the patentability rule out only those interpretations which can be derived from the patent as a whole but would clearly contradict the general technical understanding of the terms used in the claim?

3.(a) When assessing compliance with Article 123(2) EPC, must a term used in a claim be assessed against all interpretations that make technical sense to the skilled reader on the basis of the claim alone?
3.(b) If the answer to question 3.(a) is “no”, is it sufficient that only the interpretations of the subject-matter of the claim established against the background of the patent specification as a whole are directly and unambiguously derivable from the application as filed?

Final comments

It remains to be seen whether the Enlarged Board of Appeal will accept the referral. If it does accept the referral, then the questions may be modified by the Enlarged Board of Appeal before they are answered.

In the meantime, the EPO has already confirmed that it will continue examination and opposition proceedings while referral G 1/26 is pending and that Examining and Opposition Divisions will continue to apply the practice outlined in the EPO guidelines.

Given the importance of this case on claim interpretation from the perspective of added subject-matter, this case is certainly one to watch.

Related articles

• Claim interpretation: emerging trends on what “consulting the description/drawings” in G1/24 may mean: https://dycip.com/g124-claim-interpretation-consult
• G1/24 and claim interpretation: consulting the description/drawings may broaden a claim: https://dycip.com/g124-claim-description  

Case details at a glance

Jurisdiction: EPO
Decision level: Enlarged Board of Appeal
Parties: Philip Morris Products SA (applicant) and Yunnan Tobacco International Co Ltd (opponent)
Citation: G1/24
Date: 18 June 2025
Decision: https://dycip.com/epo-g1-24  

Jurisdiction: EPO
Decision level: Technical Board of Appeal
Parties: ArcelorMittal (applicant) and POSCO (opponent)
Citation: T 0873/24
Date: 03 February 2026
Decision: https://dycip.com/epo-t0873-24