On July 31, 2025, Acting USPTO Director Coke Morgan Stewart released a memo instructing the agency “that applicant admitted prior art (AAPA), expert testimony, common sense, and other evidence that is not ‘prior art consisting of patents or printed publications’ (collectively, ‘general knowledge’) may not be used to supply a missing claim limitation.”
The Director’s guidance comes on the heels of multiple Federal Circuit decisions this year interpreting 35 U.S.C. § 311. While Section 311 defines the permissible scope of prior art that may form the basis for petitioned invalidity grounds, Director Stewart’s guidance is not founded in Section 311 and instead finds footing in 37 CFR § 42.104(b)(4) (“Rule 104(b)(4)”). The memo directs Board panels to “enforce and no longer waive” the Rule 104(b)(4) requirement that a petition “must specify where each element of the claim is found in the prior art patents or printed publications relied upon.”
Although the most recent memorandum aims to establish clearer boundaries for the use of AAPA, it remains vague regarding the granularity with which Rule 104(b)(4)’s requirements will be enforced. 35 U.S.C. § 103 suggests that general knowledge may, to some extent, be employed to render obvious any minor distinctions between the prior art and a challenged patent claim. However, it is unclear whether future enforcement of Rule 104(b)(4) will necessitate that every minor element of a single claim limitation be expressly disclosed in a prior art patent or printed publication. Until panel decisions provide more guidance, petitioners would be well advised—as always—to support even minor elements of all claim limitations with explicit support in the prior art, and patent owners should diligently identify and challenge any gaps that are filled solely through appeals to general knowledge.
This application of Rule 104(b)(4) goes into effect for any petition filed on or after September 1, 2025.
Background on Use of AAPA in IPR Petitions
Over the past five years, the Federal Circuit and the USPTO have alternated in shaping the boundaries of how petitioners may rely on AAPA to challenge patent validity in inter partes reviews (IPRs).
In Koninklijke Philips N.V. v. Google LLC, the Federal Circuit considered the question under 35 U.S.C. § 311(b), which limits the scope of IPRs to invalidity grounds under 35 U.S.C. §§ 102 and 103 “and only on the basis of prior art consisting of patents or printed publications.” 948 F.3d 1330, 1337 (Fed. Cir. 2020). The Federal Circuit found that, despite general knowledge falling into neither category, general knowledge could still be relied upon to supply a missing claim limitation. It reasoned that the obviousness inquiry under 35 U.S.C. § 103 “turns not only on the prior art, but whether ‘the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious to a person having ordinary skill in the art.’” Citing a long history of Federal Circuit decisions, the Court explained that such an inquiry into whether any differences would have been obvious “necessarily depends on such artisan’s knowledge.”
Follow-on memoranda by both USPTO Director Andrei Iancu and Director Kathi Vidal, in August 2020 and June 2022, respectively, were largely consistent with this decision. The memoranda explained that AAPA could be used “in combination” with other prior art patents or printed publications to support an obviousness argument, including supplying a missing claim limitation that was generally known. Direct Vidal specifically instructed that the Board not exclude reliance on AAPA based on the number of limitations for which AAPA was used. Both Directors—like the Federal Circuit—focused on the interpretation of Section 311, though both Directors additionally noted that 37 CFR 42.104(b)(4) did not narrow Section 311 or foreclose the limited uses described in the memoranda.
As a result of these memoranda, the Board adopted an “in combination” rule for determining whether a petitioner’s reliance on AAPA was permissible under Section 311. Specifically, in Qualcomm Incorporated v. Apple Inc., the Board determined that AAPA does not form the basis of a ground in violation of Section 311(b) if the ground relies on the AAPA “in combination with prior art patents or printed publications.” IPR2018-01315, 2022 WL 19835716, at *9-12 (PTAB Nov. 10, 2022). On appeal, the Federal Circuit rejected this categorical rule, concluding that a blanket application of such a standard was not the proper legal inquiry. But the Federal Circuit merely repeated previous holdings that the appropriate question under Section 311 was whether a petitioner had used AAPA as “the basis or part of the basis” for its invalidity ground—without addressing how such a question might be answered.
It was only in Shockwave Med. Inc. v. Cardiovascular Sys., Inc. that the Federal Circuit finally provided any kind of data point for determining the extent to which AAPA could be used under Section 311. No. 23-1864 (Fed. Cir. July 14, 2025). Affirming its original decision in Koninklijke, the Federal Circuit held that AAPA may be important evidence of general background knowledge and—critically—that “general background knowledge can be used to supply a missing claim limitation.”
Acting Director Stewart’s July 31, 2025 Memorandum
Just two weeks after the Federal Circuit’s Shockwave decision, Acting Director Stewart released her memorandum regarding “Enforcement and Non-Waiver of 37 C.F.R. § 42.104(b)(4) and Permissible Uses of General Knowledge in Inter Partes Reviews.” Rule 104(b)(4) identifies requirements of a petition, including that a petition “specify where each element of the claim is found in the prior art patents or printed publications relied upon.” Acting Direct Stewart explains that “[a]s a practical matter, enforcement of Rule 104(b)(4) means that applicant admitted prior art (AAPA), expert testimony, common sense, and other evidence that is not ‘prior art consistent of patents or printed publications’ (collectively, ‘general knowledge’) may not be used to supply a missing claim limitation.” The memorandum limits the use of general knowledge to supporting a motivation to combine or demonstrating how a skilled artisan would have understood a prior art reference’s disclosure as teaching a claim limitation.
By basing this new guidance in Rule 104(b)(4), Acting Director Stewart’s attempts to sidestep any tension with previous Federal Circuit and USPTO guidance. She describes the USPTO’s previous Iancu and Vidal memoranda as inconsistent with the Federal Circuit’s Qualcomm decisions concerning the use of AAPA to supply a missing claim limitation—but the decisions are not clearly inconsistent on that point specifically. While the Federal Circuit explained that general knowledge may not form the basis of a petitioned ground and took issue with any kind of categorical rule as to whether AAPA formed the basis of a petitioned ground, the Federal Circuit did not go so far as to say that general knowledge cannot supply a missing claim limitation. Indeed, in Shockwave, the Federal Circuit dispelled any doubt on this point by holding—based on Koninklijke—that general knowledge may be used to supply a missing claim limitation. Acting Director Stewart relegates the Shockwave decision to a footnote in her memorandum, noting only that enforcement of Rule 104(b)(4) “as applied in some cases, may be narrower than 35 U.S.C. § 311(b).”
Perhaps in an attempt to further distance this guidance from the previous analysis of Section 311, Acting Director Stewart implies that Rule 104(b)(4)’s requirements are imported into 35 U.S.C. § 312, because under Section 312(a)(4) a “petition filed under section 311 may be considered only if…the petition provides such other information as the Director may require by regulation.”
Key Takeaway
While Acting Director Stewart opines that enforcement of Rule 104(b)(4) in the prescribed manner will “provide certainty to the parties, the Board, and the public, and [ ] allow for the efficient administration of the Office,” the most recent guidance still lacks clarity.
While both the USPTO and Federal Circuit agree that general knowledge cannot be the basis of a petitioned ground, the most recent memorandum is unclear as to what level of granularity Rule 104(b)(4) will be applied. Rule 104(b)(4)’s exact language requires that each “element” be identified and Acting Director Stewart states that AAPA may not be used to supply a missing “limitation.” But generally, each piece of a claimed system or each step in a claimed method can be (and often is) broken down into sub-elements that define the precise metes and bounds of that piece or step. So, the pertinent question remains as to whether general knowledge may be used to supply any of the sub-elements of a limitation.
For example, consider a limitation claiming a flexible wire connecting two widgets. Where a prior art reference discloses a wire—of uncertain flexibility—connecting two widgets, it is unclear if the most recent guidance regarding Rule 104(b)(4) forecloses the argument that general knowledge of one in the field would render it obvious to make said wire flexible. That is, is it sufficient that the prior art reference discloses the wire connecting two widgets and that flexibility was clearly within the general knowledge of a POSITA? Or is it Director Stewart’s guidance that to comply with Rule 104(b)(4), one must find a prior art patent or printed publication that explicitly discloses a flexible wire and incorporate that reference into the petitioned ground?
While Acting Director Stewart provides that “[g]eneral knowledge may still be used in an IPR to support a motivation to combine or to demonstrate the knowledge of a person having ordinary skill in the art,” the only example of how this knowledge may be used is context for supporting what a POSITA would have understood to be taught by the printed prior art. But this solitary example does not instruct whether every sub-element of a claim limitation, however trivial or obvious, must be found in a prior art patent or printed publication.
Until further guidance emerges from the Office and from the Federal Circuit, petitioners should assume that general knowledge—including applicant-admitted prior art and expert testimony—cannot supply even the most trivial of claim language. Petitioners should expect that the Board will be less receptive to hand-waving attempts or heavy reliance on experts for details of a limitation, even if those details were objectively well-known in the art. It would, therefore, be prudent for petitioners to find support in printed prior art for each substantive detail of the claims. For experienced petitioners already self-imposing such a rigorous need for support, there may be relatively little changes except the formal inclusion of supporting references in the invalidity ground. But with the potential need to include additional references in an invalidity combination, petitioners may find the statutory word limit a little more strenuous.
Patent Owners should have already been on the lookout for under-supported details of key claim limitations. However, this most recent guidance now leaves potentially no wiggle room for Board panels to fill gaps in the petition by crediting expert testimony or general knowledge. Patent Owners should identify and highlight in a preliminary response any now-impermissible reliance on general knowledge, including AAPA or expert testimony. They should also remain vigilant for instances in which Board panels improperly rely on general knowledge to conclude that a claim limitation is obvious.
