For some time, claim interpretation appeared to diverge between the Unified Patent Court (UPC) and the European Patent Office (EPO).
Both systems agree on one fundamental proposition: the wording of the claims is the starting point, and the description and drawings must be taken into account when interpreting them. The UPC Court of Appeal established this principle in February 2024 in NanoString v 10x Genomics. In June 2025, the Enlarged Board of Appeal of the EPO subsequently adopted a remarkably similar conclusion in G 1/24.
Yet, despite this common starting point, the two systems have not always shared the same logic, in particular where a claim term is given a narrow definition in the patent description.
In this article, we compare the approaches taken by the UPC and the EPO and consider how the recent decision G 1/25 may bring them closer together.
1. The UPC uses the patent as its “own lexicon”
For the UPC, the patent specification should be used as a specialized dictionary for understanding the invention. This principle has been reiterated in numerous decisions over the past three years.
Importantly, a definition provided in the patent specification may be used to interpret a term appearing in a claim even where this results in a narrower meaning than its ordinary technical meaning.
A particularly clear example is AGFA v Gucci (UPC_CFI_278/2023), where the Hamburg Local Division interpreted the term “achromatic” according to the specific definition in paragraph [0021] of the patent, leading to a much narrower construction than might otherwise have followed from the ordinary wording of the term.
More recently, in InterDigital v Disney (CFI_UPC_86/2025), the claim itself did not state that the sets of chroma and luma partition types had to differ. Nevertheless, the Mannheim Local Division relied on the definition given in the description and construed the claim as requiring the two sets of partition types to be different.
Another example can be found in Amgen v Sanofi/Regeneron (UPC_CoA_528/2024 and 529/2024). The claim required an antibody that “binds to the catalytic domain of a PCSK9 protein”, without specifying in the claim the structural boundaries of that domain. The UPC nevertheless interpreted the “catalytic domain” as the region consisting of amino acid residues 123 to 419 of human PCSK9, relying on the claim wording read together with the patent description.
2. The EPO: an apparent asymmetry
Until recently, the position before the EPO appeared different.
In 2025, G 1/24 established that the description and drawings must always be consulted when interpreting claims for the purposes of Articles 52 to 57 EPC. Yet, this decision did not explain what weight should be given to a definition in the description where that definition narrowed an apparently broader claim term.
In internal guidance issued to examiners in 2025 and reported by IPKat, examiners were essentially instructed to continue the existing practice. In particular, where a broad claim term was given a narrower definition in the description, the narrower definition should be treated as a possible fall-back position, rather than necessarily as controlling the meaning of the claim. The inconsistency was to be resolved by amending the claims or by broadening the description.
This cautious approach was also reflected in the case law of the Boards of Appeal following G 1/24. Most strikingly, in T 1999/23 issued in July 2025, the description expressly gave a claim term a narrower definition than its ordinary technical meaning. Yet, the Board held that G 1/24 did not allow that restrictive definition to narrow the claim.
Similar reluctance to interpret a claim narrowly on the basis of the description can be seen, for example, in T 1645/22, T 1561/23, T 1465/23 and T 2027/23.
The 2026 Guidelines (F – IV – 4 – 4.2) reflect this asymmetry. They state that the description and drawings cannot be relied upon to read into a claim a restrictive feature not suggested by its wording. Conversely, where the description provides a special broad definition of a term used in a claim, the claim must be interpreted in the light of that broader definition.
The claims are the starting point and the basis for assessing the patentability of an invention under Arts. 52 to 57. The description and any drawings are always referred to when interpreting the claims, and not just in the case of a lack of clarity or ambiguity (G 1/24).
However, when assessing patentability, the description and drawings cannot be relied on to read into the claim a restrictive feature not suggested by the wording of the claim.
If, on the other hand, the description provides a special broad definition of a term used in a claim, the claim must be interpreted in the light of that broad definition when assessing patentability, provided this interpretation is technically meaningful.
Read literally, this produced a curious asymmetry: the description could broaden the meaning of a claim term (potentially to the detriment of the proprietor when novelty or inventive step was assessed) but could not narrow that same term.
This difference should be seen against the different procedural contexts: during EPO examination, a lack of clarity may be cured by amendment under Article 84 EPC, whereas the UPC generally has to construe the granted claim as it stands. Moreover, UPC claim interpretation usually takes place in an adversarial context, where the alleged infringer may actively argue for a narrow construction in order to fall outside the scope of the claim, while the proprietor may seek a broader construction.
3. A change of direction at the EPO
Against this background, one decision stood out as adopting a different approach. T 0439/22, decided after G 1/24, held that where the description contains a definition of a claimed term, both its broadening and its limiting aspects must be taken into account.
This approach has now been confirmed by the Enlarged Board of Appeal itself in G 1/25, which expressly relied on T 0439/22 when setting out the general principles of claim interpretation following G 1/24 :
A person skilled in the art reading the claim in the context of the description and drawings will try to take a definition found in the description at face value. As long as the definition is technically reasonable and complies with the overall teaching of the claims, description and drawings, the skilled person will read terms in the claim in the sense of the definition, taking into account both the broadening and limiting aspects (see T 439/22 of 11 December 2025, points 3.4 and 6 of the Reasons. (point 10)
Although G 1/25 primarily concerned the adaptation of the description following claim amendments, the Enlarged Board expressly presented these statements as general principles of claim interpretation.
To conclude, G 1/25 appears to bring the EPO significantly closer to the approach already developed by the UPC. Both now recognise that the description may determine the meaning of terminology used in the claims, including where this results in a narrower construction.
However, an important question remains: where is the boundary between interpreting a term in the light of the description and reading an additional limitation into the claim?
This is precisely one of the issues now pending before the Enlarged Board in G 1/26. The referral asks whether a feature disclosed only in the description or drawings may be read into the meaning of a granted claim, in particular where this results in a restrictive interpretation of the terms used in the claim. G 1/26 may therefore provide the next piece of the puzzle and clarify whether the apparent convergence between UPC and EPO claim interpretation is complete.
In any event, these developments are a reminder that definitions in the patent description should be drafted with particular care. A definition inserted in the specification may ultimately determine the scope of the claim, in either direction. As AI increasingly assists patent drafting, this is perhaps the right time to remember that the description is not harmless background text and that one carefully (or carelessly) drafted definition may later determine the scope of the claim.
September 2026
Contributing author
