Sean Hutchinson

February 2026

Background

The Enlarged Board of Appeal’s decision in G 1/23 caused a significant change in practice at the European Patent Office (“EPO”), resulting in a product made publicly available before the priority date which the skilled person could not have reproduced now being citeable as prior art.

The effect of G 1/23 on the assessment of novelty is clear: such a non-reproducible product is prior art, but it may nonetheless be difficult to demonstrate the product is novelty-destroying if its features cannot readily be determined.

However, questions were raised about the effect of G 1/23 on the assessment of inventive step. In particular, G 1/23 led many to ask whether the skilled person would attempt to modify a product they could not reproduce, and thus whether such a non-reproducible product can be taken as the closest prior art.

We reported in our article of December 2025 that one decision of the Boards of Appeal issued after G 1/23 (T 1044/23) had addressed this issue, holding that a non-reproducible product can be taken as the closest prior art. However, another recent decision (T 1719/21) has now reached a similar conclusion, and provides additional helpful insight into this important aspect of European patent law.

Recent Developments

In T 1719/21, the proprietor argued a non-reproducible product could not be the closest prior art because “it would be unrealistic and necessarily contaminated by hindsight” to conclude the skilled person would have attempted to modify a product they could not have made.

The Board, however, disagreed.

Specifically, the Board held that to identify the closest prior art, one should search for a prior art disclosure which represents a “realistic or promising” starting point for the skilled person trying to address the aims of the claimed invention. In the case of a product claim, this may be a publicly available product which the skilled person could have modified to address the aims of the invention, even if the skilled person may not have known how to manufacture that product itself.

The Board added that only once the closest prior art has been identified should one consider whether it would have been obvious to the skilled person to have modified it to arrive at the claimed invention. In assessing this, the Board held, the non-reproducible nature of a starting product may be taken into account. For example, if the skilled person would have needed to know how that product was made to enable them to make the required modification, then the non-reproducible nature of the starting product is likely to lead to an inventive step being acknowledged.

Some Examples

The above principles are perhaps best illustrated by way of example, and one such example was given by the Enlarged Board of Appeal itself in G 1/23 (see Reason 96 of that decision).

Specifically, the Enlarged Board suggested it would have been obvious to a skilled person attempting to make a less sweet version of Coca-Cola® to have started from a glass of Coca-Cola® and to have then added lemon juice to it. However, the Enlarged Board suggested it would equally not have been obvious how to make a drink having the same taste as Coca-Cola® but not including sugar or caffeine, as this would have required knowledge of the Coca-Cola® recipe (which is, of course, a closely guarded secret).

In the case of T 1719/21, the product taken as the closest prior art was a copolymer. The parties agreed that the only potential feature of claim 1 that may provide novelty and an inventive step over this copolymer was a specific fluorine content recited in the claim. The fluorine content of the prior art copolymer was disputed between the parties. Ultimately, the Board decided it could not conclude the copolymer of the prior art had the fluorine content recited in the claim, and thus held the claimed subject matter to be novel. The Board also noted the specific fluorine content recited in the claim conferred a technical advantage, and thus held that the claimed subject matter involves an inventive step too.

Conclusions

The change in practice following G 1/23 is significant, with non-reproducible products now being citeable as prior art at the EPO. Nonetheless, the manner in which such products should be treated when assessing inventive step is still being determined.

T 1719/21, like T 1044/23 before it, offers helpful insight into this matter, indicating that a non-reproducible product can be the closest prior art, but noting the non-reproducible nature of the product may nonetheless affect obviousness of the claimed subject matter as a solution to the objective technical problem.

T 1719/21 additionally suggests the EPO is aligning itself with the European Union’s Unified Patent Court (“UPC”) in terms of how the closest prior art is to be selected, as evidenced by the Board’s decision that the closest prior art should represent a “realistic” starting point.

Whilst the case law in this area is still developing, there appears to be a consistent message from these recent decisions of the Boards of Appeal: when assessing inventive step at the EPO, what matters is what was available to the skilled person and how that would realistically have been used to attempt to so