Practical Considerations for Jepson Claims
Pine IP Firm
April 27, 2026
A Jepson claim is a claim format that divides the claim into a “preamble corresponding to the prior art” and an “improved feature part.” For example, it has a structure like “In a device comprising A, B, and C, the improvement comprises D.” In U.S. practice, 37 CFR 1.75(e) presents the format for an improvement claim in the order of a preamble, the phrase “wherein the improvement comprises,” and the novel/improved part.
The biggest advantage of a Jepson claim is that it clearly shows the inventive contribution. It allows for an intuitive explanation to the examiner of “what is the existing technology and what is the improvement.” Therefore, it can be helpful in responding to examinations in cases where the differentiation is clear, such as simple structural improvements, part replacements, or partial process improvements.
However, in practice, a Jepson claim is closer to a format that “clearly and narrowly reveals the improvement points of the invention” rather than a format that “increases the possibility of registration.” In other words, rather than directly applying it to a core independent claim that requires securing a broad scope of rights, it is advisable to consider it limitedly for auxiliary claims, preliminary claims for examination response, or when necessary for overseas response strategy.
In Korean practice, the preamble of a Jepson claim is not automatically treated as prior art. KIPO materials explain that even in Jepson-style claims, the invention must be defined by the entirety, including the preamble, and the mere fact that it is stated in the preamble should not be considered as public knowledge.
The Supreme Court, in a 2017 en banc decision, also ruled that the background art in the specification or the fact that it is stated in the preamble of a claim does not automatically mean that the technology is prior art before the filing date. It is limited to cases where the applicant clearly intended to indicate it as prior art, considering the entire specification and prosecution history. Furthermore, it was judged that this presumption could be rebutted if there was evidence of error.
However, practitioners should not over-rely on this point. If you definitively state in your response brief that “all preambles are prior art” or “the present invention is solely characterized by D,” it can be used as unfavorable prosecution history in a later invalidity trial or infringement lawsuit. When drafting Jepson claims, the wording of the claims and the expressions in the response brief must be designed together.
In U.S. practice, the risk is more direct. The USPTO MPEP explains that drafting claims in the Jepson format is treated as an implicit admission that the subject matter of the preamble is prior art of others. However, it also states that this implication can be rebutted if there are other reliable reasons, such as responding to double patenting rejections.
Therefore, it is risky to submit the same claim as filed in a Korean application directly to the U.S. simply because the Jepson format is permissible in Korea. Especially for a portfolio intended for U.S. continuation applications, re-examinations, IPRs, or infringement litigation, Jepson claims can result in the entire preamble being considered self-admitted prior art.
The 2025 Federal Circuit case, In re Xencor, is particularly important in Jepson claim practice. The court ruled that the limited preamble of a Jepson claim must also be supported by sufficient written description.
This ruling puts a brake on the approach of “it is sufficient to write only the improvement, and the preamble is prior art, so there is no need to write it in detail.” The court viewed the invention of a Jepson claim as the entire “improvement applied to the prior art,” not just the improvement itself, and therefore explained that the entire claim, including the preamble, must be supported by the specification.
In particular, in fields with low predictability or broad technical scope, such as biotechnology, chemistry, AI model structures, and semiconductor processes, preamble expressions like “known antibody,” “known neural network,” or “known etching process” can increase the risk of insufficient description.
When reviewing Jepson claims, the following order is safe:
First, **design independent claims in a general format first**. Before artificially dividing the core structure of the invention into a preamble and a feature part, securing a broad and natural independent claim as a whole combination should be prioritized.
Second, if using the Jepson format, **minimize the preamble**. The preamble should only include the components necessary to understand the application target or technical field of the invention, and unnecessary components should not be made to appear as “prior art.”
Third, **sufficiently explain the preamble components in the specification**. Especially if there is a possibility of U.S. filing, instead of treating the preamble as “obviously known,” the specification should describe what the component is, how a person skilled in the art understands it, and how the improvement is combined with that component.
Fourth, **moderate the expressions in the response brief**. Instead of definitively stating “the preamble is prior art,” expressions that clarify the context of comparison, such as “when compared with the cited invention, the differentiating technical features of the present invention are...” are safer.
Fifth, **decide in conjunction with the overseas filing strategy**. Even if an interpretation is possible in Korea that the preamble does not automatically become prior art, in the U.S., the Jepson format itself can act as an unfavorable admission. Therefore, if PCT or direct U.S. filing is planned, it is advisable to manage Jepson claims as a separate set.
The following examples are hypothetical cases for explanation.
Example of General 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.
Example of Jepson Claim
1. A cleaning brush comprising a handle and a head portion, wherein the improvement comprises a resilient pad disposed on the head portion and including a plurality of raised ribs.
In this example, “a cleaning brush comprising a handle and a head portion” is the preamble, and “a resilient pad including a plurality of raised ribs” is the improvement. If the differentiating point of the invention lies in the structure of the resilient pad on the head portion, rather than the entire brush, the Jepson format can quickly convey the invention's point to the examiner. However, caution is needed in U.S. applications, as this preamble may be treated as an implicit admission of prior art. The USPTO MPEP explains that drafting claims in the Jepson format can be interpreted as an admission that the preamble subject matter is prior art of others.
Somewhat Risky Jepson Claim Example
1. A data processing method comprising: receiving input data; and classifying the input data using a trained neural network model, wherein the improvement comprises: calculating a confidence score based on intermediate layer outputs of the neural network model; and invoking an auxiliary model if the confidence score is below a threshold.
This wording may seem clear at first glance, but the entire “data processing method comprising: receiving input data; and classifying the input data using a trained neural network model” can be perceived as prior art. In particular, in U.S. applications, there is a risk that the preamble will be interpreted as unnecessarily broad admitted prior art.
Direction for Revision
1. A data processing method comprising the steps of:
receiving input data;
generating a first classification result for the input data using a first neural network model;
calculating a confidence score based on intermediate layer outputs of the first neural network model; and
invoking a second model to generate a second classification result if the confidence score is below a threshold.
For software or AI inventions, it is often safer to structure the entire process as a general claim, as shown above, rather than using the Jepson format. Especially in the AI field, the expression “known neural network model” can become a burden later in terms of written description, inventive step, and claim scope interpretation.
Risky Jepson Claim Example
1. A therapeutic method comprising administering a known antibody to a patient, wherein the improvement comprises the Fc region of the antibody including a specific amino acid substitution.
This wording is very risky because it is unclear to what extent the preamble “know known antibody” and “therapeutic method” are actually known. In the 2025 U.S. Federal Circuit case, In re Xencor, it was also ruled that the preamble of a Jepson claim, if it is a limitation, must be supported by sufficient written description.
Direction for Revision
1. A composition comprising an antibody that binds to a C5 protein, wherein the antibody comprises M428L and N434S amino acid substitutions in the Fc region, and wherein the composition has an increased in vivo half-life compared to a corresponding antibody lacking the amino acid substitutions.
Alternatively, if method of treatment claims are permissible in the jurisdiction, the following approach of directly describing the entire composition is safer:
1. A method of treatment comprising administering an antibody that binds to a C5 protein to a patient, wherein the antibody comprises M428L and N434S amino acid substitutions in the Fc region, and wherein the antibody has an increased in vivo half-life compared to a corresponding antibody lacking the amino acid substitutions.
The key point is that not only the “improvement needs to be written,” but the subject to which the improvement is applied must also be sufficiently supported by the specification. The In re Xencor ruling clarified that the burden of written description also applies to the preamble of Jepson claims.
Jepson claims are not a “bad claim format” but a “claim format with limited use.” It is advisable to choose it only when the improvement of the invention is extremely clear, there is a strategic need to reveal the relationship with the prior art, and the reduction in scope of rights and admission risk resulting from it can be accepted.
Conversely, if a broad scope of core rights needs to be secured, if there is a possibility of obtaining rights overseas, especially in the U.S., or if it is unclear whether the preamble technology is truly known, it is safer to prioritize general combination claims and leave the Jepson format as an auxiliary option.
Ultimately, the core of Jepson claims is not the format but **record management**. The claim wording, the description of background art in the specification, the logic of comparing prior art in the response brief, and the set of overseas application claims must all be consistent. Since even a small expression can determine the scope of rights and validity later on, Jepson claims must be designed from the initial filing stage with the dispute stage in mind.
