FEATURE ARTICLE: Defending & Preventing AI Hallucination
Author: Professor Michael H. Hoeflich, PhD, Editor-in-Chief
Legal Editor: Carrie E. Parker
This article is featured in Volume 7, Number 4 of the Legal Ethics and Malpractice Reporter, published April 30, 2026.
In last month’s Legal Ethics & Malpractice Reporter, we outlined the increasing number of cases involving the submission of hallucinated case law by lawyers and law firms and the increasing imposition of sanctions by courts under Federal Rule of Civil Procedure 11 and related state rules. Here, we examine the defenses that have been raised by attorneys and firms that have submitted fake citations and how courts have reacted to them.
I didn’t Know What I was Doing
The defense of ignorance has proven to be a bad choice. Courts have cited many rules when addressing the issue of hallucinated law—most frequently FRCP 11 and Rules of Professional Conduct 1.1, 3.1-3.4, and 5.1-5.4. None of these rules mentions intent. Accordingly, pleading lack of intent to be technically incompetent or lack if intent to misinform the court is not likely to be effective. It might also anger the court.
For example, in Mattox v. Product Innovations Research LLC, when a lawyer insisted he did not know ChatGPT would alter the citations in a brief he asked the platform to make more persuasive, the court acknowledged the attorney’s actions were “not born of deceit.” 807 F.Supp.3d 1341, 1349 (E.D.OK 2025). Still, they “displayed a reckless disregard for the obligation to ensure that what is filed in federal court is true, verified, and worthy of the public trust,” warranting sanctions “both to redress the specific harm and to deter recurrence.” Id.
The deliberate submission of false authority to the court is, of course, particularly offensive. But courts will not excuse the inadvertent submission of false or inaccurate authority when the current legal landscape is full of warnings regarding the risks of AI-generated material.
It Wasn’t Me
To date, lawyers have not avoided sanctions by noting that someone else actually prepared the document they signed.
Citing FRCP 11, courts generally find that any lawyer who signs a document is responsible for what it contains. This rule has been relied upon in sanctioning local counsel who submit filings prepared by co-counsel for whom they have sponsored pro hac vice admission to practice. See, e.g., Mattox, 807 F.Supp.3d at 1351-1352; Wadsworth v. Walmart Inc., 348 F.R.D. 489, 498-99 (D. Wyo. 2025); Lifetime Well LLC v. IBSpot.com Inc., No. CV 25-5135, 2026 WL 195644, at *9 (E.D. Pa. Jan. 26, 2026).
Even lawyers who did not sign the offending documents may be subject to discipline. KRPC 5.1 requires lawyers with managerial and supervisory authority to “make reasonable efforts to ensure that the firm has in effect measures giving reasonable assurance that all lawyers in the firm conform to the rules of professional conduct” and makes those lawyers responsible for the professional misconduct of their subordinates under specified circumstances. Accordingly, if any attorney in a firm is found to have violated KRPC 3.3’s obligations of candor, then his manager or supervisor may be on the hook as well. See N.Z. v. Fenix Int’l Ltd., No. 8:24-CV-01655-FWS-SSC, 2025 WL 3626155, at *4 (C.D. Cal. Dec. 12, 2025).
I’m Sorry
The white shoe law firm of Sullivan & Cromwell recently made headlines for the “apology letter” submitted in In re Prince Global Holdings Limited, et al., No. 26-10769 (Bankr. SDNY). Kelsey Vlamis, “AI hallucinated — and now an elite law firm is profusely apologizing to a federal judge,” Business Insider (Apr. 21, 2026), available at https://www.businessinsider.com/sullivan-and-cromwell-apologizes-ai-hallucinations-court-filing-2026-4; Karen Freifeld & Mike Scarcella, “Sullivan & Crowell law firm apologizes for ‘AI’ hallucinations in court filing,” Reuters (Apr. 21, 2026), available at https://www.reuters.com/legal/litigation/sullivan-cromwell-law-firm-apologizes-ai-hallucinations-court-filing-2026-04-21/. Acknowledging that a prior submissions included AI-generated citations that were fabricated (including wrong reporters and incorrect pin cites) and misquoted holdings, the letter stated “deep[] regret” that the error-filled filing occurred—noting “[t]he Firm’s policies on the use of AI were not followed in connection with the preparation of the” document.
In some cases, contrition may help mitigate the sanction and diminish reputational damage, but it is not a defense.
Conclusion
To date, we have seen nothing operate as a full defense when a filed document contains erroneous authority attributable to AI hallucinations. There being no “cure,” courts insist on prevention.
READ THE FULL ISSUE OF LEMR, Vol. 7, No. 4
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