Which Parts of an Expert’s ChatGPT History Related to Preparing Expert Report Must Be Disclosed?

From Judge Anne Traum (D. Nev.) Monday in Villanueva v. Las Vegas Metro. Police Dep’t (the underlying lawsuit alleges a jail corrections officer abused plaintiff when plaintiff was arrested):

Plaintiff Jose Villanueva sued Defendants Francis Soriano and the Las Vegas Metropolitan Police Department (“LVMPD”), for violations of state and federal law that occurred while he was detained at Clark County Detention Center (“CCDC”)….

Plaintiff’s expert witness, Tom Melton, testified in his October 1, 2025 deposition that he relied upon ChatGPT, an artificial intelligence program, to assist him with researching and drafting his expert report…. Defendants filed a motion to compel the production of Plaintiff’s expert Tom Melton’s ChatGPT history log with respect to his preparation of his expert report….

A party or its “representative” may invoke the trial preparation privilege to shield against the discovery of “documents and tangible things that are prepared in anticipation of litigation or for trial.” Fed. R. Civ. P. 26(b)(3)(A). Subject to Rule 26(b)(4) and upon a threshold showing of discoverability, “substantial need,” and “undue hardship,” trial preparation documents may be subject to discovery. However, any court-ordered production of trial preparation materials must be structured to “protect against disclosure of the mental impressions, conclusions, opinions, or legal theories of a party’s attorney or other representative.”

Expert witnesses may also invoke discovery privileges related to their draft reports. In their expert report, expert witnesses are required to include “the facts or data considered by the witness in forming” their opinion. Rule 26(a)(2)(B)(ii) was amended in 2010 to limit disclosures to “facts or data considered,” instead of previous language on “data or other information” that was interpreted by many courts as requiring the disclosure of “all attorney-expert communications and draft reports.” The rules distinguish between the required disclosure of facts or data considered, and an expert’s drafts of their report, which are protected from discovery….

The court held that parts of the history log had to be disclosed:

First, the Court will consider which parts of Melton’s history log constitute “facts or data” under the meaning of Rule 26(a)(2)(B)(ii) that must be disclosed as part of his expert report. The Ninth Circuit’s interpreted Rule 26(a)(2)(B)(ii) and the accompanying advisory committee notes to find that “the requirements should ‘be interpreted broadly’ to encompass ‘any material considered by the expert, from whatever source, that contains factual ingredients.'” Republic of Ecuador v. Mackay, 742 F.3d 860, 869 (9th Cir. 2014). The court emphasized that disclosure required facts or data “considered” by the expert in forming their opinions, “‘not only those relied upon by the expert.'”

The legal case summaries generated by ChatGPT constitute “facts or data” that Melton considered and must be disclosed under Rule 26. This Court finds persuasive the reasoning in Hirata v. S. Nevada Health Dist. (D. Nev. 2016). The Hirata court found that an expert’s failure to disclose summaries of thousands of pages of deposition materials as “facts and data” considered in creating their report violated Rule 26(a)(2)(B)(ii). Even if the summaries were provided by the party calling the expert and the expert “only consulted the summaries as a quick-reference guide, he still considered the summaries within the meaning of Rule 26.”

Plaintiff explains that Melton used the AI software to ask “for a case summary of certain controlling court cases on excessive force.” Because Melton generated case summaries and “consulted” them to reach his expert opinion on excessive force, the ChatGPT-generated case summaries constitute “facts or data” that are subject to disclosure under Rule 26….

Because AI-generated case summaries are “facts or data,” disclosure under Rule 26 requires the disclosure of all case summary responses supplied by ChatGPT. As Defendant correctly contends, the history log is the only place where Defendant can review alleged “hallucinated case citations … quotes … and references to broad legal standards” that Melton relied upon, or at least considered, to reach his opinion.

But the court held that other parts were privileged and thus protected from mandatory disclosure:

The Court finds it was clearly erroneous or contrary to law to order the production of the entirety of Melton’s ChatGPT history, because Melton’s: 1) questions and prompts to ChatGPT, 2) use of the program to create a deposition outline, and 3) creation of a draft report are all protected from disclosure….

First, the Court finds that Melton’s questions and prompts to ChatGPT are not subject to disclosure. The threshold question is whether questions are “facts and data” considered by Melton that are subject to disclosure under Rule 26(a)(2)(B)(ii). The Court finds that a question is not something that an expert can “consider” or “rely” upon as “facts or data” in reaching their opinion, just as an expert would not “consider” or “rely” upon their online research queries.

Next, the Court will determine whether Melton’s questions and prompts are protected by any discovery privileges. Whether construed as part of an expert’s draft report under Rule 26(b)(4)(B) or trial preparation materials under Rule 26(b)(3)(A), in any case, discovery into Melton’s questions to ChatGPT would be impermissible. Based on the text of Rule 26 and accompanying advisory committee notes, the Ninth Circuit stated that “the driving purpose of the 2010 amendments was to protect opinion work product—i.e., attorney mental impressions, conclusions, opinions, or legal theories—from discovery.” While Rule 26(b)(3)(A) provides a qualified privilege for an attorney or their representative’s trial preparation materials (work product), disclosure cannot include the “mental impressions, conclusions, opinions, or legal theories of a party’s attorney or other representative concerning the litigation.” Fed. R. Civ. P. 26(b)(3)(B). The Court finds Plaintiff’s argument persuasive that Melton’s questions and prompts to ChatGPT reveal his “mental impressions or strategy … as to what issues he found of particular importance” and Melton’s theory of the case. Because Melton’s questions are not “facts or data” and impermissibly reveal his mental impressions and theories, the Court finds that it was clearly erroneous or contrary to law to order the production of this portion of the log….

[A] deposition outline is [also] not “facts or data” within the meaning of Rule 26. Instead of using ChatGPT’s outputs to inform his expert opinion, Melton used ChatGPT’s responses to structure his preparation for his deposition and trial. Plaintiffs should not have to disclose the portion of the history log related to deposition preparation…. Melton’s creation of a deposition outline would impermissibly disclose his “mental impressions, conclusions, opinions, or legal theories,” because such an outline would reveal Melton’s focus, priorities, or areas of concern to address in the deposition and at trial.

Lastly, … prompts to create a draft report on “certain issues, such as qualifications of the opposing expert or analysis of the opposing expert’s report” is squarely within the protections of an expert’s draft reports. Rule 26(b)(4)(B) mandates the protection of expert drafts “regardless of the form in which the draft is recorded.” Melton testified to sometimes copying and pasting the outputs of ChatGPT into his own report. It appears that Melton’s usage of the ChatGPT responses was to assist in his writing and analysis of his expert report, rather than to create “facts or data” to consider in forming his opinion.

Defendant argues that ChatGPT’s responses are not Melton’s “own generation of a report,” and is therefore not protected as an expert draft report under Rule 26(b)(4)(B). The Court finds that Melton’s creation of a draft report on ChatGPT is protected as a draft report, because Melton testified that some of this information was directly incorporated into his own written report. Even if the ChatGPT output is not a draft report protected under Rule 26(b)(4)(B), it would still be mental impressions protected from disclosure under Rule 26(b)(3)(b). As addressed above, the ChatGPT responses would provide direct insight into Melton’s “mental impressions” and “legal theories” that he considered relevant in a report….

The court also concluded that any privilege wasn’t waived through disclosure to ChatGPT, “[b]ecause ChatGPT is not a person, but was an application used in this instance as a research, drafting, and editing program.” And the court noted that “many of Defendant’s concerns about Melton’s methodology and reliance on ChatGPT are appropriate to address at trial as matters of impeachment.”