EPO maintains ST.26 sequence listing requirement for divisionals but compromises on excess page fees

The implementation of the new sequence listing format ST.26 by the EPO raises added matter risks for applicants. The ST.26 standard came into force in July 2022 and applies to all new European applications filed after this date, including divisionals. The applicant may therefore be required to convert the ST.25 sequence listing of a parent application into a ST.26 sequence listing for a divisional. However, converting from ST.25 to ST.26 has the potential to add matter. 

DNA Maine Coon
The Institute of Professional Representatives before the European Patent Office (epi) raised the added matter issue with the EPO last year (IPKat). The EPO did not initially consider the risks to applicants sufficient to justify a change in policy (IPKat). More than a year later, and following continued pressure from epi, the EPO has now indicated its intention to waive excess page fees for adding an ST.25 sequence listing to the description of a divisional, in the manner of claim-like-clauses. This compromise will lower the cost burden for applicants seeking to avoid the added matter risk from ST.26. The EPO nonetheless ultimately holds firm to the principle of requiring the ST.26 format for all new divisional applications. 

What are sequence listings and why are they needed?

There is an international requirement for biological sequences disclosed in a patent application to be provided in a sequence listing document. The sequence listing serves two purposes. First, the sequence listing facilitates the ability for the patent offices to search for the disclosed sequences in the prior art. Second, it allows the sequences in the patent application to be uploaded to public sequence databases. 

The ST.26 "Big Bang" date

On the hyperbolically termed Big Bang date of 1 July 2022, the old international standard for sequence listings, ST.25, was replaced by the new ST.26 standard.  The shift to ST.26 aimed to increase public access to patent sequences. It also requires additional information about certain types of sequences to be included in the sequence listing. 

ST.26 applies to new applications filed on or after 1 July 2022, regardless of priority date. For the purposes of international patent applications, the filing date is the PCT filing date. Patent offices have discretion over whether ST.26 applies to new divisional applications filed after the Big Bang date (FAQ: Implementation of WIPO ST.26, 31). The EPO has chosen to follow the recommendation of WIPO that ST.26 should apply to new divisionals (OJ  2021, A97). Therefore, regardless of when an application was first filed, ST.26 applies to any new EP divisional application filed after July 2022. The UK, by contrast, does not apply the ST.26 standard to divisionals of applications filed under the ST.25 regime. 

EPO under fire for its approach to ST.26 sequence listings 

Last year, epi wrote to the EPO raising concerns that requiring an applicant to convert an ST.25 sequence listings into ST.26 format for a divisional application may unavoidably add matter to the divisional. The handbook for ST.26 itself highlights scenarios in which particular care must be taken not to add matter when converting sequence listings from ST.25 to ST.26 format (Annex VII). In cases where the original ST.25 sequence listing was itself vague or unclear, the handbook notes that "compliance with ST.26, without introduction of added subject matter, is not possible" (ST.26, Annex VII, Scenario 7). epi argued that this will create legal uncertainty over the validity of divisional EP patents for years (IPKat). 

With regards to the added matter issue, the EPO responded that users could avoid any risk of added matter by filing the divisional application without a ST.26 sequence listing. Basis for the sequences in such cases could be provided by adding the ST.25 sequence listing to the description of the divisional (IPKat). The ST.26 sequence listing can then be filed after the filing date under Rule 30(3) EPC. A sequence listing filed in this way does not form part of the application as filed, and therefore cannot add matter. epi pointed out that this solution, whilst avoiding the added matter issue, may incur a late furnishing fee for the ST.26 sequence listing and excess page fees for the ST.25 sequence listing added to the description. After all, a sequence listing may contain hundreds of sequences and be many pages long.

Latest response from the EPO

Following continued pressure to address the risks and burden to applicants of the EPO's ST.26 divisional requirement, the EPO has now provided a follow-up response to epi. On the fundamental issue of whether the ST.26 format applies to new divisionals, the EPO is standing firm:

"the EPO has decided to maintain the transitional regime for divisional applications. This regime is in line with the practice of several other offices and with the internationally agreed principle that the filing date should be the reference date for the applicability of WIPO Standard ST.26"

However, as a compromise, the EPO has indicated that it will be removing the excess page fee for ST.25 sequence listings added to the description of divisonals:

"the EPO has decided to waive any additional page fees which may be due when it is used. Similarly, in cases where the divisional application is filed by reference to the parent application, the EPO will not charge any additional page fees for an ST.25 sequence listing contained in the certified copy under Rule 40(3) EPC".

The EPO indicates that the official announcement of this change will be provided in the October issue of the Official Journal. We await clarification on when the change will come into force. If possible, users may therefore wish to delay the filing of EP divisionals in order to avoid unnecessary excess page fees. The EPO notes that the late furnishing fee for filing a ST.26 sequence listing can be avoided by filing the ST.26 sequence listing before being invited to do so by the EPO. 

DNA sphynx

Final thoughts

We therefore should not expect to see any change to the requirement before the EPO that ST.26 applies to all new divisional applications, regardless of when the parent application was filed. However, the EPO has taken some measures to make it easier for applicants to avoid the risk of adding matter. Good practice going forward is therefore to include the ST.25 sequence listing in the description of newly filed divisionals, for which excess page fees will no longer apply. The ST.26 can then be filed shortly after in order to avoid the late furnishing fee. 

Tangential to this discussion is the broader question of whether the sequence listing standard requirement for patent applications is fit for purpose. The WIPO software for producing sequence listings is remarkably old-school. In the emerging era of large language model (LLM) assisted patent drafting and prosecution (IPKat), it is remarkable to this Kat that there is no better solution to the current approach for processing the sequences disclosed in a patent application (IPKat). Whilst ST.26 represents a small step towards modernising patent sequence data, the result so far appears to have been to increase the burden to applicants. As sequence data inevitably continues to grow in volume and complexity, a more contemporary solution will eventually be required. 

Further reading

Image credits: DALLE-3
EPO maintains ST.26 sequence listing requirement for divisionals but compromises on excess page fees EPO maintains ST.26 sequence listing requirement for divisionals but compromises on excess page fees Reviewed by Rose Hughes on Friday, October 27, 2023 Rating: 5


  1. EPO says the waiving of excess page fees for ST25 description pages will go into effect from the publication of the Nov 23 OJ on 30 November 2023.

  2. Now officially announced:


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