EPO Enlarged Board Concludes Oral Proceedings in G 1/25, Signals Continued Mandatory Description Adaptation

The Enlarged Board of Appeal of the European Patent Office (EPO) closed oral proceedings in referral G 1/25 on 8 May 2026, addressing whether the European Patent Convention (EPC) requires applicants and patent proprietors to adapt the description to match amended claims. No decision was issued from the bench; a written ruling is expected later this year. The referral touches a daily working assumption of European prosecution practice, and the answer will shape examiner workflows, opposition strategy, and downstream claim construction at national courts and the Unified Patent Court (UPC).

The referral originated in Technical Board of Appeal decision T 697/22, which involves a patent owned by Knauf Insulation directed to hydroponic growing media. The referring board observed that the EPC contains no explicit provision requiring the description to be brought into conformity with amended claims, and that European case law has split into two distinct lines — one treating description adaptation as obligatory under Article 84 EPC, and another holding that no such requirement exists.

The Three Referred Questions

Three questions were referred. First, where claims are amended during opposition proceedings and an inconsistency with the description arises, must the description be adapted to comply with the EPC? Second, if so, which provision of the EPC mandates such adaptation? Third, would the answer differ if the amendments occur during examination rather than opposition?

In its preliminary opinion issued in early 2026, the Enlarged Board signaled support for maintaining the EPO’s existing practice. The preliminary view on question one was that adaptation is required when the inconsistency results in non-compliance with the EPC, but not where the inconsistency itself does not give rise to such non-compliance. On question two, the Board’s preliminary view was that Article 84 EPC—which requires that claims be supported by the description—provides the legal basis for the adaptation requirement. On question three, the preliminary view was that no distinction should be drawn between examination and opposition.

The Oral Proceedings

The 8 May oral proceedings brought submissions from the referring board, the applicant’s representatives, and a substantial group of amicus curiae filings. European patent attorney bodies and the IP departments of several large European corporates supported the existing practice, citing the importance of a clear public record and the role of the description in delimiting claim scope at national level. A number of applicants and industry associations, particularly U.S.-headquartered companies and certain pharmaceutical filers, argued the practice imposes unnecessary procedural cost and creates litigation risk because amended descriptions can be used against patentees during infringement and validity proceedings. According to participants and observers, the Board pressed counsel on whether Article 84 supplies a workable trigger for the adaptation requirement and how the “inconsistency” threshold should be drawn, without telegraphing where the panel would ultimately land.

Practical Consequences

If the final decision tracks the preliminary opinion, EPO examiners will retain the authority to require applicants to amend embodiments, definitions, drawing descriptions, and other parts of the specification that fall outside amended claims. This is a deeply embedded part of European prosecution: applicants and their representatives typically allocate substantial pre-grant time and cost to crafting the description amendments necessary to obtain a Rule 71(3) communication. A decision in line with the preliminary opinion will preserve those workflows and the budgets built around them.

If the Board departs from its preliminary opinion, the practical effect would be larger. Prosecution cost and timeline could compress noticeably, and applicants prosecuting parallel U.S., Chinese, and European applications could preserve a more unified specification across jurisdictions—an outcome long sought by global filers. National validity courts and the UPC, however, would still have the discretion to look to the original specification for claim construction, and applicants should not assume an end to the strategic significance of description content.

For now, practitioners should continue to apply the current EPO practice. That means responding to examiner adaptation requests as part of the standard pre-grant exchange, ensuring that embodiments and examples are clearly characterized as falling within or outside the amended claims, and considering how those characterizations may be deployed in post-grant proceedings. Opposition strategists should be especially attentive: G 1/25’s reach into opposition means description amendments accepted during opposition are likely to remain a fixed element of European post-grant practice.

Timing and Broader Context

Timing for the written decision has not been formally announced. Based on historical practice for Enlarged Board referrals, a written opinion is expected later in 2026 or early 2027. The EPO is also expected to revise the relevant sections of the Examination Guidelines (F-IV, 4) in step with the final ruling, after which prosecution manuals and examiner training materials will need to be updated to reflect any clarifications—including the precise contours of when an “inconsistency” triggers an adaptation requirement under Article 84.

The Enlarged Board’s G 1/25 decision will sit alongside G 1/24, in which the Board harmonised claim interpretation between the EPO and the UPC. Together, the two decisions are reshaping how the relationship between claims and description is policed across the European patent system. For applicants weighing the strategic implications of the EPC versus other jurisdictions, the combined effect should sharpen attention to specification drafting choices made years before grant.