Practical Considerations for Jepson Claims

A Jepson claim states the conventional or known elements in a preamble and then identifies the claimed improvement. A typical form is: “In a device comprising A, B, and C, the improvement comprising D.” In the United States, 37 C.F.R. § 1.75(e) describes this format.

The format identifies the asserted improvement efficiently, but it also affects claim construction, prior-art admissions, and written-description analysis. Those effects differ between Korean and U.S. practice.

Use of the format

A Jepson claim may be useful when an application concerns a discrete improvement to a well-defined device, composition, or process. It can present the point of novelty in a compact form and may simplify discussion with an examiner.

The format does not itself make an invention more patentable. It identifies part of the claim as conventional or known and can narrow the practical dispute to the improvement. A conventional combination claim should ordinarily be considered before a principal independent claim is converted to Jepson form.

Korean treatment of the preamble

In Korea, placement of an element in the preamble does not by itself establish that the element was publicly known before the filing date. The claim is assessed as a whole, including both the preamble and the characterizing portion.

In its January 19, 2017 en banc decision in Case No. 2013Hu37, the Korean Supreme Court held that a feature is not treated as publicly known solely because it appears in a claim preamble or in the background-art section of the specification. An admission may be inferred from the specification and prosecution history as a whole, but that inference may be rebutted where the statement was erroneous or other circumstances show that the applicant did not intend to acknowledge prior-art status. The court's official summary is available here.

Drafting and prosecution statements still require care. A statement that every preamble feature is prior art, or that the invention resides only in one added feature, can become part of the prosecution record even though the claim form alone would not establish public knowledge.

U.S. admitted-prior-art treatment

U.S. practice assigns a more specific evidentiary consequence to the format. MPEP § 2129 states that drafting a claim in Jepson form is taken as an implied admission that the preamble subject matter is the prior-art work of another.

The implication is not irrebuttable. The MPEP identifies circumstances in which another credible reason for the format may overcome it, including use of the format to address double patenting. It also states that an inventor's own work may not be used against the claims merely because it appears in a Jepson preamble. The applicant should nevertheless assume that the examiner, the Patent Trial and Appeal Board, and a later tribunal will examine the preamble as an admission unless the record supports a different conclusion.

A claim set prepared for Korea should therefore be reviewed before U.S. filing. A Jepson claim that creates limited risk under Korean practice can create an admitted-prior-art issue in the United States.

Written description under In re Xencor

In In re Xencor, Inc., No. 2024-1870 (Fed. Cir. Mar. 13, 2025), the Federal Circuit held that the limiting preamble of a Jepson claim must have sufficient written-description support. The applicant cannot avoid 35 U.S.C. § 112 by asserting that only the improvement requires description.

The claim at issue concerned treatment with anti-C5 antibodies having specified Fc-domain substitutions. The court held that the claimed invention was the improvement applied to the preamble subject matter, not the improvement in isolation. The amount of disclosure needed depends on the knowledge of a person skilled in the art, the predictability of the field, and the scope and novelty of the claimed subject matter. Evidence outside the application may inform what the skilled person knew, but the application must still convey possession of the claimed invention.

Xencor is particularly relevant when a preamble uses a broad technical category such as an antibody genus, neural-network architecture, semiconductor process, or chemical class. Calling the category “known” does not establish that the applicant possessed the full scope recited in the claim.

Drafting sequence

1. Draft a conventional claim first. Define the complete combination without assigning prior-art status through the claim form.
2. Identify the reason for Jepson form. Use it only when the benefit of expressly identifying the improvement exceeds the admission and scope risks.
3. Limit the preamble to necessary subject matter. Each additional preamble element can affect claim scope and the admitted-prior-art record.
4. Support the complete claim. Describe the preamble subject matter, the improvement, their interaction, and representative embodiments across the claimed breadth.
5. Control prosecution language. Distinguish the cited reference without making broader admissions than the record requires.
6. Prepare jurisdiction-specific claim sets. Review Jepson claims separately for Korean, U.S., PCT, and other national-phase practice.

Mechanical-device example

Conventional claim

1. A cleaning brush comprising a handle, a head portion, and a resilient pad disposed on the head portion, wherein the resilient pad includes a plurality of raised ribs.

Jepson claim

1. In a cleaning brush comprising a handle and a head portion, the improvement comprising a resilient pad disposed on the head portion and including a plurality of raised ribs.

The Jepson version identifies the handle and head portion as the setting for the improvement. In U.S. practice, it also creates an implied admission concerning that preamble subject matter and ordinarily makes the preamble part of the claim's limiting context.

Software and AI example

Jepson form

1. In a data-processing method comprising receiving input data and classifying the input data using a trained neural-network model, the improvement comprising calculating a confidence score from intermediate-layer outputs and invoking an auxiliary model when the confidence score is below a threshold.

This form may treat the preamble's data-receiving and neural-network classification steps as admitted prior art in U.S. practice. It also requires written-description support for the neural-network context as part of the claimed combination.

Conventional form

1. A data-processing method comprising:
receiving input data;
generating a first classification result for the input data using a first neural-network model;
calculating a confidence score from intermediate-layer outputs of the first neural-network model; and
when the confidence score is below a threshold, invoking a second model to generate a second classification result.

The conventional form does not resolve patentability, but it avoids the specific implied admission created by Jepson form and presents the claimed steps as one combination.

Chemistry and biotechnology example

Jepson form

1. In a therapeutic method comprising administering an anti-C5 antibody to a patient, the improvement comprising providing the antibody with specified amino-acid substitutions in its Fc region.

A broad preamble of this kind must be supported for its full limiting scope. In a field with substantial structural and functional variability, one disclosed antibody may not support a genus of anti-C5 antibodies.

Conventional composition form

1. A composition comprising an antibody that binds C5 protein, wherein the antibody comprises specified amino-acid substitutions in an Fc region and has an increased in vivo half-life relative to a corresponding antibody lacking the substitutions.

Whether this alternative is adequately supported depends on the actual disclosure and the applicable jurisdiction. Recasting a claim does not cure a missing written description.

Claim-set decision

Jepson form is appropriate only when the applicant intends to identify the preamble as the conventional setting for a defined improvement and accepts the resulting consequences. A principal claim directed to a broad commercial combination will often be better presented in conventional form, with narrower fallback claims available for prosecution.

The claim language, background-art discussion, specification support, response briefs, and foreign claim sets should be reviewed together. Inconsistent treatment of the preamble can affect examination, validity, and infringement analysis.