An AI plug-in took 16% off Thomson Reuters in a day; LegalZoom never won its loss back

01The trigger and the day

Anthropic’s post of 30 January opened: “Today, we’re adding support for plugins”. It released 11 plug-ins built by its own team as open source, as a research preview for paid Claude users; the legal one is described as “Review documents, flag risks, and track compliance.”¹ Reuters reported on 3 February that investors tied the selling to the plug-ins. Mike Archibald of AGF Investments said: “I think Anthropic came out with some plug-ins to tackle the legal space.” Morgan Stanley analysts wrote that most investors they had spoken to were “overwhelmingly bearish on TRI”, and Schroders’ Jonathan McMullan called the selling “a deepening structural debate”. Traders told Reuters that fear often outweighed company fundamentals.² Reuters had Thomson Reuters down nearly 18% during the session; the close was 15.67%.

Thomson Reuters reported its 2025 results two days later. Organic revenue grew 7% in the fourth quarter, and chief executive Steve Hasker said the company would “continue to scale our agentic capabilities”, pointing to “professional-grade tools built on quality content and deep subject-matter expertise.”⁵

02Eight months on

RELX first closed back above its 2 February level on 3 March. Thomson Reuters did so on 5 March and again on 3 September, after falling about 31% below it by 22 June. Wolters Kluwer fell 30.4% below by 25 June and first closed above it on 15 October.³⁴ On 15 October the three publishers rose 2.4% to 4.3% while the Amsterdam index fell 0.4%; we did not find what moved them and do not attribute it. Over the whole period the S&P 500 rose 9.8%, the AEX 13.2% and the FTSE 100 5.2%.⁴

LegalZoom reported 2025 revenue up 11% and no debt on 19 February, when Jeff Stibel, its chairman and chief executive, said: “AI is transforming how legal work starts, which is opening up new markets.”⁷ Its shares never closed above their 2 February level; the best was US$8.42 on 29 July.³ On 5 August it cut its 2026 revenue outlook from US$810–830m to US$795–805m, “reflecting the recent industry-wide shift in customer discovery away from traditional search”. Stibel said: “While demand for what we do is intact, discovery is moving.”⁸ The shares closed 30.06% lower the next day. The same day Thomson Reuters raised its 2026 organic growth outlook to about 8%, with Hasker naming “Fiduciary-Grade AI solutions” as the priority; its shares closed 9.66% lower that day.⁶³

03What the prices show, and what they do not

On 3 February the market priced the three publishers and LegalZoom alike, all down 13% to 20% on a research preview. By October they had separated. Thomson Reuters reported growth and raised its outlook; LegalZoom cut its outlook and gave its own reason, how customers find it, not the plug-in. None of the four releases we read attributes any lost revenue to Anthropic’s plug-in, and Anthropic has published no usage figures for it. The coverage on the day quoted both readings: traders saying fear outweighed fundamentals, and analysts describing a structural debate. This Note records the prices and who said what; it does not settle which reading was right.