What was hallucinated

Misrepresented: Case Law | Counsel attributed a parenthetical quotation to Mir that misstated the case's holding; Court questioned the accuracy and required explanation. || Fabricated: Case Law | Brief included a nonexistent case citation (a 'mashup' citation) that did not match any real opinion; Court treated it as an AI-style fabricated citation and faulted counsel for failing to verify.

Details

"In her declaration, Attorney Cervantes described the erroneous citation as her own inadvertent error and further implied that Westlaw’s tool may have “glitched” by erroneously producing the citation. [Dkt. 31 at ¶ 4]. Specifically, she indicates that the copy citation tool mayhave inadvertently copied the wrong citation information.Yet, that explanation seems highly improbable. The citation was incorrect in every respect and none of the sub-parts of the citation match each other, including the case docket number, reporter, pincite, court information, and date information. The likelihood of every component of a citation being simultaneously wrong due to a software malfunction in transcribing from a “correct” citation is, in the Court’s view, statistically improbable (particularly given Westlaw’s representations as to the accuracy of its tools and the apparent resources Westlaw has devoted to promoting the reputation of this tool). If one set of numbers had been transposed, or if the date were wrong, such transcription errors might be explicable. However, the fact that the party names, docket number, Westlaw citation, date, and court all failed to match, resulting in a mashup citation, cannot credibly be attributed to a software error, let alone a mistranscription or copying mistake. Rather,this Frankensteinian legal citation, stitched together from mismatched party names, docket numbers, dates, and courts, bears the hallmarks of an AI-generated hallucination, as documented in numerous published opinions and reports."

Sanction teardown · N.D. California, USA · 2025-09-05

Anthony C. Hill v. Workday, Inc. (1)

What happened

In N.D. California, USA, a filing relied on CoCounsel to help draft legal argument. The court identified the following problems with the citations in that filing:

Misrepresented (Case Law)

Counsel attributed a parenthetical quotation to Mir that misstated the case's holding; Court questioned the accuracy and required explanation.
Fabricated (Case Law)

Brief included a nonexistent case citation (a 'mashup' citation) that did not match any real opinion; Court treated it as an AI-style fabricated citation and faulted counsel for failing to verify.

Which AI tool

CoCounsel. Note: Charlotin's public database records tool attribution only where a court order, brief, or reporting on the matter states it explicitly; "unidentified" or "implied" means the record indicates AI use but does not name a specific product — we do not guess.

Outcome

Order to circulate decision in law firm; CLE

Additional detail

"In her declaration, Attorney Cervantes described the erroneous citation as her own inadvertent error and further implied that Westlaw’s tool may have “glitched” by erroneously producing the citation. [Dkt. 31 at ¶ 4]. Specifically, she indicates that the copy citation tool mayhave inadvertently copied the wrong citation information.Yet, that explanation seems highly improbable. The citation was incorrect in every respect and none of the sub-parts of the citation match each other, including the case docket number, reporter, pincite, court information, and date information. The likelihood of every component of a citation being simultaneously wrong due to a software malfunction in transcribing from a “correct” citation is, in the Court’s view, statistically improbable (particularly given Westlaw’s representations as to the accuracy of its tools and the apparent resources Westlaw has devoted to promoting the reputation of this tool). If one set of numbers had been transposed, or if the date were wrong, such transcription errors might be explicable. However, the fact that the party names, docket number, Westlaw citation, date, and court all failed to match, resulting in a mashup citation, cannot credibly be attributed to a software error, let alone a mistranscription or copying mistake. Rather,this Frankensteinian legal citation, stitched together from mismatched party names, docket numbers, dates, and courts, bears the hallmarks of an AI-generated hallucination, as documented in numerous published opinions and reports."

How Citation Safe would have caught this

Citation Safe runs three deterministic layers before a brief is filed: (1) does the citation exist against CourtListener's database of published opinions, (2) if quoted, does that exact language appear in the source, (3) does the cited case actually support the proposition it is cited for. Fabricated case citations fail Layer 1. Fabricated or misattributed quotations fail Layer 2 even when the underlying case is real. Misrepresented holdings — a real case cited for a proposition it does not support — are the target of Layer 3. None of these checks involve asking another language model whether the citation looks right; they are lookups and text-matches against the actual source, which is why a hallucinated citation has to survive a direct lookup against the authoritative source — not another model's opinion — to earn a VERIFIED stamp; our measured false-verify rate is published live at /quality.

Check a brief before you file it → · See our live false-verify rate

Source: https://www.damiencharlotin.com/documents/976/Hill_v._Workday_USA_5_September_2025.pdf, via Damien Charlotin's public AI Hallucination Cases Database (CC0).