A recent Delaware Court of Chancery decision provides a cautionary tale about the issues raised by AI hallucinations in a court filing. In Leiske v. Kidd, C.A. No. 2025-0426-CDW (LWW) (Del. Ch. July 1, 2026), the court addressed a court filing with AI hallucinations and analyzed potential consequences.
Noteworthiness of This Case
This short post intentionally does not identify the lawyers or the law firm involved, but instead provides highlights and a few takeaways from this ruling that have relevance to all litigators who use AI, or who encounter its use by other parties. Although there are other Chancery decisions that address AI hallucinations, and the court cites to other cases around the country that have dealt with the issue, this letter ruling provides noteworthy guidance about how to address this problem when it happens, and how to avoid the problem.
Brief Background
The background of this case involved an advancement suit that was decided by a Magistrate Judge in Chancery who awarded advancement. The Vice Chancellor then reviewed this matter to decide exceptions to the Magistrate’s final report on advancement–and more importantly for this blog post addressed the AI issues.
Highlights
- The issue presented to the court was how to address the problem of an answering brief that contained “fictitious citations, fabricated quotations, and hallucinated legal propositions.” See footnote 2 and accompanying text.
- The problems were exacerbated because, according to the court, when a corrected brief was filed, the corrected version did not cure all of the hallucinated or incorrect statements of law, nor did it correct the inaccurate descriptions of the cited cases. Rather it merely removed quotation marks and attributed “the oversight to a paralegal’s review.” Slip op. at 2.
- The attorney who filed the brief with hallucinations double-downed after the issue was presented to the court, and insisted on “the accuracy of the underlying legal propositions” and stated that the “cited authorities are real and support the arguments advanced” while accusing opposing counsel of “using the GenAI errors to gain a litigation advantage.” Slip op. at 3.
- In its analysis, the court referred to Court of Chancery Rule 11(b) that requires an attorney presenting a pleading or written motion to the court to certify that the “legal contentions made are warranted by existing law,” and emphasizing that an attorney’s signature on a court filing is a certification to the tribunal. Id. at 4.
- In this case the court found that although using GenAI in court filings is “not inherently problematic,” counsel in this case acknowledged that the GenAI output was “not verified” before the brief was filed. Id. See also footnote 16 (referring to prior Chancery decision addressing the use of GenAI).
- The court explained that hallucinated legal propositions raise an inference of a Rule 11(b) violation. That rule requires counsel to show cause why sanctions should not issue in this situation. See footnote 19 (citing the cases in other jurisdictions involving sanctions for submitting hallucinated GenAI citations).
- The court expressed its concern raised by the errors in the initial filing being compounded by the counsel’s response after the errors were identified.
- The court referred to Rule 11(c)(1) that provides for a law firm to be held jointly responsible for violations committed by its partners, associates or employees. Slip op. at 6.
- The court required an affidavit from the lawyer involved—and his firm—to provide a detailed explanation about how GenAI was used in this instance and what the firm’s written policies and guidelines on the use of GenAI by its attorneys and staff that were in place at the time that this mistake occurred, as well as requiring other detailed averments.
Takeaways
If a document filed with the court is found to contain errors, whether based on GenAI or other reasons, the lawyer must immediately:
- 1) notify the court promptly and submit a completely correct version of the court filing soon as possible;
- 2) take full responsibility for the mistake, and
- 3) explain to the court how the mistake occurred—and steps taken to make sure it does not happen again.
Postscript
- Although the counsel involved in this imbroglio won on the merits of the advancement action, the AI problem dwarfs any success on the merits. The problem occurred in a filing that was made in January of 2026, and seven months later the problem is only getting worse.
- The next phase of this saga is a final decision on whether to award sanctions that the court will make after receiving from the lawyer and the firm involved affidavits last week that the court required to explain why sanctions should not be imposed.
Bonus Supplement
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