On March 30, 2026, the Seventh Circuit[1] addressed sanctions for an attorney citing AI-generated hallucinations[2] and clarified the responsibilities of opposing counsel when receiving such a pleading.
In Dec v. Mullin, petitioner’s counsel cited two non-existent cases and included a false quotation in a “standard of review” section of an appellate brief.[3] During oral argument,[4] counsel denied using AI but later filed a letter admitting the cases were copied and pasted from another unlocatable brief. Counsel apologized for failing to verify the citations. While the Seventh Circuit admonished the attorney, it declined further sanctions because the errors were unintentional, counsel was contrite, and the hallucinations supported an undisputed legal standard.
The Court’s Response to AI‑Generated Errors
The court observed: “Whatever AI’s future in litigation, our concern lies with trained lawyers failing to check the accuracy of legal citations and quotations in their filings.”[5] The Seventh Circuit noted that with tools like Westlaw and LexisNexis, verifying a brief’s citations is more straightforward than ever.[6] The court reminded the bar that these errors waste judicial and party resources and critiqued opposing counsel for failing to catch the inaccuracies.[7]
The court wrote: “That opposing counsel also failed to catch these errors and bring them to our attention also gives us pause, albeit to a lesser degree.”[8] While the court did not impose a formal duty upon counsel to audit an adversary’s work, it signaled that the legal system’s integrity depends on shared vigilance.
The Seventh Circuit also noted that while AI tools offer benefits to practitioners, those efficiencies do not absolve attorneys of their fundamental duty to verify the accuracy of their work and submissions to the courts. As the court noted, the “peril” of abdicating professional care remains with the attorney.
[1] Dec v. Mullin, No. 25-2417 (7th Cir. Mar. 30, 2026).
[2] Hallucinated cases are fictitious cases with inaccurate facts or legal propositions generated by AI systems. See Zach Warren, GenAI Hallucinations Are Still Pervasive In Legal Filings, But Better Lawyering Is the Cure, Thomson Reuters (Aug. 18, 2025).
[3] Id. at 10.
[4] Oral argument, Feb. 24, 2026, at 5:30–6:44.
[5] Id.
[6] Id.
[7] Id. at 12.
[8] Id. In contrast, in a recent case, In re Prince Global Holdings Limited, et al., No. 26-10769 (S.D.N.Y. Bankr. April 18, 2026), opposing counsel noticed AI-hallucinated case citations in a party’s emergency motion and notified that party of their errors. The party who relied on AI-hallucinated cases notified the court of their own errors and credited opposing counsel for flagging the issue.
