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Legal actionSeverity N: legal or test findingConfirmed: a company, official or court statement

US appeals court upheld Thomson Reuters' win over Ross Intelligence over alleged use of Westlaw headnotes to train AI

The 3rd US Circuit Court of Appeals upheld a ruling for Thomson Reuters in its copyright dispute with Ross Intelligence, rejecting Ross' argument that training its AI-powered legal search engine on Westlaw headnotes was fair use. Thomson Reuters' lawsuit accused Ross of misusing thousands of headnotes to train a competing legal search engine. A Delaware federal judge had earlier rejected Ross' fair use defense, and Ross shut down its platform in 2021, citing litigation costs. The court's reasoning is currently sealed.

What the AI did

Ross Intelligence was accused of training its AI-powered legal search engine on thousands of headnotes copied from Thomson Reuters' Westlaw legal research platform. The search engine was built to find relevant court opinions for user queries, and it competed with Westlaw. A lower court judge found that Ross took the headnotes to make it easier to build a competing tool.

First reported September 30, 2026 · Added to the register October 4, 2026 · 1 source

Developer
Ross Intelligence
Affected
Thomson Reuters (Westlaw)
Country
United States
When it happened
Not stated in the sources
First reported
September 30, 2026

What this means for you

Could this affect you?

Possibly, if you train AI on content you do not own or have not licensed

Companies that train AI on content they have not licensed may want to follow this case: the appeals court upheld the ruling against Ross Intelligence's fair use defence, though its reasoning is sealed.

What to check

  • Audit where your AI training data comes from and whether it is licensed.
  • Do not rely on a fair use defence when training material comes from a competitor's product and is used to build a competing tool.
  • Track the appeals ruling once its reasoning is unsealed.

Areas of your AI programme this touches

Data protection and privacy
Every fact and its source (5)
  1. Lower court findingDelaware federal judge found Ross' use was not transformative
    ““So Ross’s use is not transformative.””[1]
  2. Consequence for defendantRoss shut down its platform in 2021
    “Ross shut down its platform in 2021, citing the costs of Thomson Reuters’ litigation.”[1]
  3. Status of reasoningAppeals court reasoning is sealed
    “The appeals court’s reasoning for its decision is currently sealed.”[1]
  4. Appellate ruling3rd Circuit rejected Ross' fair use defense and upheld the ruling for Thomson Reuters
    “A US appeals court on Tuesday upheld a ruling for information services company Thomson Reuters”[1]
  5. Material used for trainingThousands of Westlaw headnotes
    “It accused Ross of misusing thousands of headnotes to train its competing AI-based legal search engine.”[1]

Sources

  1. Appeals Court Upholds Thomson Reuter Landmark Win in AI Training Lawsuit
    insurancejournal.com · September 30, 2026

How this record is classified. Severity N: a legal action or test finding, not a harm. Evidence: Confirmed, meaning a company, official or court statement.

The facts in At a glance and in Every fact and its source are quoted from the sources listed. The summary, What the AI did and What this means for you are written from those sources and checked against them automatically before publication. Records reflect what has been disclosed, not everything that has happened. Incidents are found through news feeds and the GDELT Project.

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