G 1/25, Take Three: Anything You Leave in the Description May Be Used Against You

A patent's future construction can be shaped before an infringement action begins. At the European Patent Office, a passage retained, rewritten or deleted during opposition may influence how a court later reads the amended claims. When the description is settled at oral proceedings, choices with lasting consequences for enforcement may have to be made under immediate procedural pressure.

G 1/25, handed down by the Enlarged Board of Appeal on 3 September 2026, sets the conditions under which an amendment to the claims obliges the proprietor to adapt the description.1The decision's practical consequences have already been examined on this blog by Adam Lacy and Thorsten Bausch. Miquel Montañá has also highlighted the strategic implications of description amendments for future enforcement. The question pursued here is how to prepare those choices: which passages deserve scrutiny, when an opponent should seek their removal, and what earlier adaptations may mean for a patent about to be asserted.

Read from the litigation side, the decision does more than fix a threshold for adaptation. It makes the description a governed document, gives the Office a standard for governing it that is itself a rule of claim construction, and leaves the product of that exercise to circulate through every infringement action brought on the patent for the rest of its life. It does so from the first amendment filed before an examining division, because the Enlarged Board answered the question about examination proceedings with a plain no.2

The core of it fits in three sentences. The order names Articles 52 to 57, 76(1), 83, 84, 123(2) and 123(3) EPC as the provisions whose breach makes adaptation necessary. All of them but one correspond to a ground of revocation under Article 138(1) EPC, to which Article 65(2) UPCA confines revocation before the Unified Patent Court. The exception is Article 84, so the one category of inconsistency the Office alone can address is the one a court can receive only as a question of construction.

Where prosecution and litigation are handled under separate mandates and separate budgets, the document that decides the second is produced in the first, and, after G 1/25, it is produced under conditions of time pressure that the decision expressly endorses.

What the Enlarged Board Actually Held

The referral came from Board 3.3.02 in T 697/22, an opposition appeal between Knauf Insulation and Rockwool concerning a hydroponics growing medium.3Claim 1 of auxiliary request 1E had been amended in a way that changed the definition of the binder. Paragraphs [0013] and [0016] of the description, as amended before the opposition division, still described the binder in the earlier terms. The Referring Board considered that this combination could not satisfy Article 84 EPC, and asked whether the EPC requires the description to be adapted, and if so on what legal basis.

The Enlarged Board answered that adaptation is necessary where, and only where, the inconsistency introduced by the claim amendment causes non-compliance with Articles 52 to 57, 76(1), 83, 84, 123(2) or 123(3) EPC.4There is no free-standing duty of tidiness. The Board said so in terms: the EPC does not require adaptation "merely for the sake of formal concordance", an inconsistency having no legal effect requires no adaptation at all, and Article 84 EPC imposes no general obligation to remove from the description all matter not reflected in the claims.5

The operative move is the definition. An inconsistency exists where statements in the description or drawings suggest an understanding of a claim incompatible with the claim's apparent meaning, and that incompatibility cannot readily be resolved by applying G 1/24.6The test is whether the skilled person, reading the claim in the light of the description and drawings, would be left in real doubt as to what the claim means. Unclaimed embodiments are not, by themselves, an inconsistency. Uncertainty about whether an embodiment is claimed or not is.

Two further holdings matter more than their length suggests. The Board confirmed that claim interpretation under G 1/24 is a unitary reading of claims, description and drawings, not a sequential exercise in which the description is consulted only once ambiguity is found, and it extended that method beyond the patentability provisions to Article 84 itself. The same passage sets a limit that deserves as much attention as the method: the description and drawings may affect the meaning the skilled person attributes to the claim wording, but they cannot be used to impose on the claim a limitation or expansion for which the claim wording provides no basis.7And the Board noted that the interpretative approach and the definition of inconsistency are not contingent on the existence of an amendment, even though the answers given are confined to the amendment situation.8The reasoning is general. The dispositive part is not. That gap is where the argument will now be conducted.

The obiter remarks are the part a litigator should read twice. Amending the claims and adapting the description are, procedurally, a single step. In appeal proceedings the description is "almost always finalised in the oral proceedings before the Board", and the Enlarged Board said that nothing in its decision calls for a change to that practice.9In the referring case itself, the proprietor did try to improve its position at the hearing, filing a new description with paragraphs [0013] and [0016] deleted. The Board refused to admit it because it was late.10A description that later courts will read was thus settled by an admissibility ruling, on a filing made in the room, on a text that had not been prepared as a litigation document.

The List That Matters Is the One Article 84 Is On

The asymmetry stated at the start of this article is worth setting out in full, because it carries most of the argument. Article 138(1) EPC lists the grounds on which a European patent may be revoked, and Article 65(2) UPCA confines revocation before the Unified Patent Court to those grounds and to Article 139(2) EPC. Want of patentability, insufficiency, added matter and extension of protection are all on it. Clarity is not, and never has been. G 1/25 does not put it there.

The consequence is not that the Article 84 cases are the harmless ones. It is the reverse. Where an inconsistency is caught by Article 83 or Article 123(2), the Office and the court are working on the same material with the same label, and a defendant can raise the point squarely. Where it is caught only by Article 84, the Office holds a power no court shares, and the court receives the same textual conflict in the only form available to it, as a question of construction.

Article 123(3) on the Enlarged Board's list deserves separate notice, and less weight than a first reading gives it. The Enlarged Board added it for completeness, observing that whether an inconsistency of the sort it considered can give rise to issues under Articles 83, 76(1) and 123 EPC is "more theoretical than practical", and that it expects such issues to arise rarely, if ever.11What remains is narrower, and still worth having: the Enlarged Board did not exclude that such an inconsistency may, in a particular case, become relevant to compliance with those provisions. Under Article 68 EPC a patent amended in opposition is treated as having had its amended effects from the outset, so the description that emerges from the opposition is the description a court will read. Whether a paragraph deleted at the hearing changes anything in a given infringement action is a question to be analysed on the facts of that action, before the forum seised of it.

The Description Audit: Five Objects, Five Different Fates

The description is not one thing. It is five: the definition, the orphan embodiment, the advantage statement, the residual clause and the drawing. Each of the five behaves differently at the Office after G 1/25, and differently again before a court.

The first object is the definition. G 1/25 endorses the approach that a skilled person takes a definition found in the description at face value, so long as it is technically reasonable and consistent with the overall teaching, and reads the claim term accordingly, in both its broadening and its limiting aspects.12A definition is therefore the most powerful sentence in a patent that is not a claim, subject to the limit the Enlarged Board states in the same breath: it operates only so far as the claim wording gives it something to work on. It is also the object most likely to survive an adaptation exercise untouched, because it rarely creates doubt. It resolves it, in whatever direction it was drafted.

The second object is the orphan embodiment, the one that no longer falls within the amended claims. G 1/25 is explicit that its presence is not, by itself, an inconsistency. It stays. It may serve the patentee as material for arguments on equivalents and on the technical contribution, and the defendant as the demonstration that the patentee described, and then abandoned, the very thing now said to infringe. Which way it cuts is a question of fact in the action, not a consequence of the decision.

The third object is the advantage statement, the recital of technical effect. This is the object G 1/25 makes genuinely dangerous. The Board gave the example itself: where a claim has been amended to meet Article 56 EPC but the description still expresses a technical teaching reflecting the claim before amendment, and that statement conflicts with the fulfilment of the inventive-step requirement, the inconsistency has to be removed.13Advantage language written to sell the invention in 2013 becomes, in 2026, an inventive-step admission attached to a claim the drafter never contemplated.

The fourth object is the residual clause, the consistory or claim-like statement that mirrors the claim as filed. What changes is the test. A consistory clause tracking the pre-amendment claim will often leave the reader in real doubt about which text defines the invention, and doubt is now the criterion.

The fifth object is the drawing. G 1/25 assimilates drawings to the description at every point of its reasoning, without exception. A figure showing a feature the amended claim no longer requires, or a configuration the claim now excludes, stands on the same footing as a paragraph saying so in words. An adaptation exercise that touches only the text is therefore incomplete, and the point is sharpest in mechanical and industrial files, where reference numerals do the definitional work and the figures carry geometries, arrangements and relative positions the claim never recites. A defendant arguing non-infringement will reach for them early. Nobody has to translate a drawing.

The Parameter and the Range

The referring case is the cleanest illustration available, which is convenient, because it is also the one whose facts are on the public record. The amendment redefined a binder. Two paragraphs of the description continued to describe the binder otherwise. Nothing more exotic than that was needed to produce a referral to the Enlarged Board.

The recurring version of this problem in chemistry and materials is the parameter whose measurement method lives only in the description. A claim limited during opposition to a viscosity, a particle-size distribution, a loss on ignition or a degree of cure takes its meaning from the protocol described in the specification. Where the description sets out two protocols, or a protocol with a temperature range wide enough to give different results at its ends, the skilled person may be left in real doubt whether a given product falls within the claim. That is an inconsistency on the G 1/25 definition, and before the UPC it is also the infringement case. Which protocol the amendment was intended to invoke is a question of fact about a document, and it is cheaper to settle in the weeks before the hearing than after service of a statement of claim.

Second medical use and dosage-regimen patents carry the same mechanism in a more acute form, because their descriptions are written to cover a therapeutic space far wider than the claim that eventually survives. A specification teaching administration of about 10 mg to 100 mg, and describing the advantages of the whole range, may emerge from opposition with a claim confined to a single dose and an unamended description still praising the range. Under G 1/25 that description does not have to be cut unless it puts compliance in issue. Left in, the range language may support an argument on equivalents at the top of the claim and an obviousness argument at the bottom of it. And where the description recites a technical effect for the full range while the claim was narrowed precisely because that effect could not be shown across it, the statement of effect is the kind of inconsistency the Enlarged Board's own example says has to go.

Telecoms and Standards: The Description as an Essentiality Document

For patents declared essential to a standard, the description performs a function no other document performs. It is where the invention is tied to a technical problem which the standard also solves, and it is frequently where a particular release of the standard is named. Amendments in opposition narrow the claim toward the standard, and the description, written years earlier against a different release, stays where it was.

The implementer's argument follows. If the description explains that the invention addresses a problem the standard solved in a different way, the mapping from claim to specification may not be the mapping in the claim chart. The licensor's answer is that the description defines the terms in the licensor's favour, which holds only if somebody drafted it that way and nobody deleted it. Adaptation decisions on standard-essential patents may therefore carry consequences for essentiality, taken in a forum where essentiality is not in issue. A licensor with a portfolio in opposition should be able to say which of its files are being reshaped this quarter, and who read the claim charts before the description was settled.

The Same Grid, Read From the Other Side

An opponent runs the audit for a different purpose and may reach the opposite decision. Pressing for the deletion of a broad description passage tends toward a narrower construction in the infringement action that follows, and that is worth having. Leaving it in produces an inconsistency argument now and a real-doubt argument later, and that may be worth more.

The choice depends on facts the opposition file does not contain: whether the opponent's own product sits inside or outside the passage, whether it will still be on the market when a claim is issued, whether the opponent intends to clear the way or to keep the patent narrow and alive. Those are commercial facts, and they belong to a mandate that opposition counsel does not necessarily hold.

This is the asymmetry G 1/25 creates, and it favours whoever notices it first. The Office will not force the tidying. Each side is therefore free to argue for the version of the description it wants the court to read, subject only to persuading the Board. That is a litigation choice made in an administrative proceeding, and it is one that can be made by default.

The Stock You Already Hold

The grid applies to files now in opposition. The harder question concerns the patents already maintained in amended form.

Before G 1/25 the Boards were divided, the Referring Board having identified two lines of case law on whether the EPC requires the description to be brought into line with amended claims.14Descriptions cut on the stricter view were cut for a formal concordance the Enlarged Board has now said the EPC does not require. Two questions follow, and neither is rhetorical. First, on which of those patents did the proprietor delete matter it would not have had to delete, and does the deletion read, on the face of the published B2 specification, as a deliberate narrowing of scope? Second, on which of them does the file show the proprietor arguing for a construction it will need to contradict in an infringement action?

What weight a court will give to that record is not settled. The Court of Appeal of the Unified Patent Court has not decided whether the prosecution history may be taken into account in determining the scope of protection: in VusionGroup v Hanshow it left the question open, the parts of the examination file relied on by the parties disclosing nothing that altered its analysis.15An issue left open by an appellate court is not an issue that has gone away, and G 1/25 has just made the file materially richer, because the Office will now be recording, opposition by opposition, findings about what claims mean.

Any patent about to be asserted is therefore worth reading in its B2 form against its A publication, with the deletions marked.

The Objection, and What the Decision Leaves Open

The serious objection to all of this is that it overstates the reach of an administrative decision. Article 84 binds the Office and nobody else. National courts and the Unified Patent Court construe under Article 69 EPC and its Protocol, applying the EPC as a source of law under Article 24(1)(c) UPCA but owing no deference to EPO practice on description adaptation. And since G 1/25 requires less cleaning than the practice it replaces, descriptions will emerge from opposition more cluttered, not less, which is hardly a revolution for litigators.

The objection is right on every proposition and wrong in its conclusion. More surviving description is more construction material, in a system whose appellate court has held that the description and drawings must always be used as explanatory aids for the interpretation of the claim, and not only to resolve ambiguity.16The volume of material a court must read has just increased, and the filter that used to reduce it has been removed. Meanwhile the deletions that are still made are made under a test, real doubt as to the meaning of the claim, which is a construction test in everything but name. Whether or not a court is bound by what the Office concludes, the Office is now producing construction findings on the record of every contested opposition in Europe.

G 1/25 confines its answers to inconsistencies introduced by claim amendments, while stating that the principles apply more generally. Three questions therefore remain. It does not decide whether the same standard governs a granted patent whose claims are not amended in opposition, though it says the same considerations may arise. It does not decide whether an amendment to the description alone can offend Article 123(3) EPC, although it puts that provision on the list. And it says nothing, because it was not asked, about the weight a court should give to an adaptation performed under its own test.

They will be answered by the Boards and, in due course, by the Court of Appeal in Luxembourg. In the meantime the practical consequence of the decision is available now and requires no further authority.

Prosecution counsel should not have to decide alone what the description says once the claims move. The audit of the five objects belongs before the oral proceedings, and litigation counsel belongs in the room where the description is settled. Choose the description before choosing the forum, because by the time the forum is chosen the description has already decided part of the case.

• 1Enlarged Board of Appeal, G 1/25, decision of 3 September 2026, ECLI:EP:BA:2026:G000125.20260903, Order.
• 2G 1/25, Answers to the Questions, Question 3, and Reasons, "Question 3".
• 3Technical Board of Appeal 3.3.02, T 697/22, interlocutory decision of 29 July 2025, referring Questions 1 to 3; European patent application No. 07704142.4, "Hydroponics growing medium"; proprietor Knauf Insulation, opponent ROCKWOOL A/S. The facts summarised here are taken from G 1/25, Summary of Facts and Submissions, points I to VI.
• 4G 1/25, Order, and Answers to the Questions, Questions 1 and 2.
• 5G 1/25, Reasons, "The meaning of inconsistency", "Inconsistency and Article 84 EPC" and "Conclusions on adaptation of the description".
• 6G 1/25, Reasons, "The meaning of inconsistency".
• 7Enlarged Board of Appeal, G 1/24, decision of 18 June 2025, ECLI:EP:BA:2025:G000124.20250618, Order; G 1/25, Reasons, "The relevance of decision G 1/24 to the present referral" and "Interpretation of Article 84 EPC".
• 8G 1/25, Reasons, "Amended and unamended claims".
• 9G 1/25, Reasons, "Obiter remarks: when to amend the description".
• 10G 1/25, Summary of Facts and Submissions, points III and IV, referring to T 697/22, paras 9.1 and 9.4.
• 11G 1/25, Reasons, "Further Articles of the EPC and inconsistencies".
• 12G 1/25, Reasons, "The relevance of decision G 1/24 to the present referral", citing T 439/22 of 11 December 2025, points 3.4 and 6 of the Reasons.
• 13G 1/25, Reasons, "Inconsistency and Articles 52 to 57 EPC".
• 14G 1/25, Summary of Facts and Submissions, points VII to XXI, summarising the two lines of case law identified in the Referral Decision, and Reasons, "Interpretation of Article 84 EPC".
• 15UPC Court of Appeal, 13 May 2024, UPC_CoA_1/2024, VusionGroup (formerly SES-imagotag) v Hanshow, order on provisional measures, where the Court left open whether the prosecution history may be taken into account in interpreting the claims.
• 16UPC Court of Appeal, 26 February 2024, UPC_CoA_335/2023, NanoString Technologies v 10x Genomics and President and Fellows of Harvard College, headnote 2, as rectified by order of 11 March 2024.