Sunstar Engineering Europe GmbH v. Ceracon GmbH, Mannheim Local Division, June 6, 2025 (UPC_CFI_745/2024)
The UPC has recently clarified its strict approach to amending counterclaims for revocation in patent litigation. The Mannheim Local Division ruled that parties cannot introduce new prior art or grounds for revocation after the initial filing of a counterclaim, if the omission was caused by an oversight in a prior art search. This decision underscores the importance of comprehensive preparation at the outset of UPC proceedings.
Background
Sunstar Engineering commenced infringement proceedings against CeraCon, and, in response, CeraCon filed a counterclaim for revocation of the patent (EP4108413), which included prior art references and arguments. Two months later, CeraCon sought to introduce an additional piece of prior art, arguing that they had only recently become aware of the new material, despite a diligent prior art search by a reputable firm. CeraCon contended that allowing the amendment would not prejudice Sunstar, particularly given that the prior art is Sunstar's own patent application, which was filed by the same representatives representing Sunstar in these proceedings. CeraCon further argued that the requirements of an amendment of case according to Rule 263 Rules of Procedure (RoP), if applicable to counterclaims for revocation, should at least be applied generously, and that neither the UPCA nor the Rules of Procedure explicitly exclude the introduction of new grounds for invalidity in the Reply to the Defense to a counterclaim for revocation. According to Rule 263.2 RoP, the court shall grant leave to amend a case only if (a) the amendment in question could not have been made with reasonable diligence at an earlier stage, and (b) the amendment will not unreasonably hinder the other party in the conduct of its action. Sunstar opposed the request and, in the alternative, requested a two-month deadline to respond to the new prior art.
Decision
The Mannheim Local Division rejected the request to amend the counterclaim. Rule 263 RoP applies equally to counterclaims for revocation as it does to infringement claims, prohibiting the late introduction of new prior art or grounds. The court emphasized that all grounds and supporting documents must be included in the initial counterclaim, as required by Rule 25 RoP. The interests of the counterdefendant in having certainty in preparing its defense and not having to defend itself against a new attack for the first time in the rejoinder outweighed the counterclaimant's interest in introducing new arguments at a later stage, regardless of the reasons for the initial omission.
Key takeaways
This decision signals a strict procedural approach by the UPC. This contrast with more flexible practices in some national courts, such as Germany, where submission of prior art in later stages of the proceedings is sometimes permitted. Litigants in the UPC should therefore ensure that all relevant grounds and supporting documents are identified and included when a counterclaim for revocation is filed. UPC proceedings require thorough and early preparation.
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