How Far Does Rule 26 Go?: Key Considerations When Working with Experts

The Federal Rules of Civil Procedure have evolved to protect privileged communications between attorneys and their clients, and, under Rule 26, they also extend work-product protection to certain expert-witness communications, protecting the mental impressions, legal theories, and strategy of counsel. Rule 26’s protection of draft reports prepared by expert witnesses—rendering them undiscoverable—is specifically designed to protect attorney work product, as such drafts often reflect mental impressions or strategic input of counsel. However, the question remains: Just how far does the scope of these protections go?

In Sonate Corp. v. Beyond Meat, Inc., No. 1:23-cv-10690-IT, 2025 U.S. Dist. LEXIS 98592 (D. Mass. May 23, 2025), the court examined the scope of Rule 26’s protections for draft reports. There, Beyond Meat, Inc. moved to compel two pilot surveys conducted by Vegadeplhia’s expert witness involving a trademark-infringement dispute. The expert acknowledged in his deposition that he used the pilot surveys to refine the final survey disclosed in his expert report, though the report itself did not reference the pilot version.

The Massachusetts District Court granted the motion, concluding that the pilot surveys did not qualify as “drafts” protected under Rule 26(b)(4)(B)’s work product doctrine. It reasoned that because the expert considered the pilot survey when refining his final survey, this fell within Rule 26(a)(2)(B), encompassing disclosure of all “facts or data considered.” The court cited to a decision from the District of Delaware, finding the reasoning in Robocast, Inc. v. Apple, Inc., No. 11-235-RGA, 2013 U.S. Dist. LEXIS 201317 (D. Del. Sept. 18, 2013) instructive. There, the court found that it was “difficult if not impossible to believe that an expert whose opinions are predicated upon the creation of a statistically-meaningful effort could have, in the statistical sense, completely ignored the data that had been previously collected by him, even where the data from prior surveys had been deleted and the expert attested that he could no longer remember them at the time he drafted his reports.” Thus, the court ordered the defendant to produce the prior surveys in question.

What might this decision mean for the future of maintaining privilege for expert witnesses? To start, it does not affect privileged communications and work product that falls squarely within Rule 26’s protections on undiscoverable information. Rather, it signals a cautionary shift in how courts may interpret the boundaries of work-product protection when it comes to expert-witness materials. This ruling narrows the protective scope that attorneys may otherwise expect when working with expert witnesses, particularly in the preliminary review or testing phase. Counsel must remain aware that internal testing, preliminary data, or pilot studies—if considered in forming final opinions, may be discoverable despite Rule 26’s protections against revealing an attorney’s mental impressions or legal strategy. Going forward, attorneys should be cautious of how initial expert drafts are used and approach the discovery phase with heightened awareness that even “discarded” work may become fair game to the opposing party.