A woman named Natalia, identifying herself as being with a company called “2077AI,” was looking to source what she described as a “fairly large order” of books. Attached was a spreadsheet listing more than 3,000 ISBNs along with instructions to match titles, prepare quotes and estimate shipping costs directed to China.

De Vries barely looked at it, dismissing the message as spam or phishing without reading past the first few lines. It wasn’t until weeks later, when a Dutch journalist investigating the procurement request contacted him, that he learned of the request’s connection to artificial intelligence.

“I was shocked!” said de Vries, who provided Fortune with the email and subsequent spreadsheet containing 3,001 titles, mostly published between 2020 and 2021 by academic publishers like Emerald Publishing, Elsevier, Wiley, Routledge and Oxford University Press, and ranging from business and education to engineering, public policy and medicine. “Very unusual,” de Vries said. “That’s why I regarded the request as spam or phishing.”

De Vries wasn’t the only one. He told Fortune several other Dutch antiquarian booksellers received the same request and, like him, dismissed it. (They didn’t take “it seriously” and “considered it as scam,” he said). While the inquiry had little effect on his business, he said, it could have been a different story for booksellers who specialize in selling secondhand books at scale.

“I deal in old and rare books,” de Vries said, adding he rarely receives book orders by e-mail and if he does it’s at most for only one book. “These books are expensive and exclusive. So I do not do bulk trade.”

AI’s appetite for books

The email De Vries received never mentioned artificial intelligence or explained what the books would be used for., but it surfaced as AI companies increasingly look beyond the open internet for high-quality written material to train large language models.

Last summer, public attention to AI companies’ use of books intensified when court records revealed Anthropic had purchased millions of physical books, removed their bindings, scanned them and discarded the originals to build a searchable digital library used to train its AI models in what internal documents called “Project Panama,” according to The Washington Post. The process, known as “destructive scanning,” involves cutting the spine from a book so its pages can be fed through high-speed scanners before the remaining physical copy is discarded.

The case later settled after a federal judge ruled that using legally purchased books to train AI models constituted fair use under copyright law. Separate claims involving Anthropic’s downloading of books from the LibGen and PiLiMi online libraries were resolved through the settlement.

According to an Anthropic spokesperson, Claude models are trained on a mix of publicly available web data, commercially acquired datasets and internally generated data. Anthropic purchases books through regular commercial markets, and none of its data acquisition programs acquire or destroy rare or antiquarian books.

The hidden supply chain

The court records showed what happened after books were acquired, not how companies source millions of physical volumes in the first place.

Earlier this year, 404 Media reported that ISBNdb, a company best known for maintaining metadata tied to International Standard Book Numbers (ISBNs), the unique numerical identifiers encoded in the barcodes found on most books, had begun advertising services to help AI labs source bulk printed book purchases ranging from 1,000 to 1 million books. According to the report, the company’s website said the service was tailored to “LLM training needs” and “delivered at the scale AI demands.”

The webpages have since been removed. ISBNdb later told Fortune the service was never launched, it never purchased or scanned books for AI companies and the webpages reflected an exploratory concept rather than an active business. Similar reports have emerged in Germany and Switzerland, where local media reported that secondhand booksellers received unusual bulk orders for highly specialized books that appeared inconsistent with traditional collecting or resale. Zoom Books, a Canadian company identified in some of the reports, denied these allegations and told Swiss broadcaster SRF the purchases were part of its regular recycling and trading model.

For an industry built on algorithms, the email offers a rare glimpse into something much more tangible: the physical supply chain of books that may ultimately power AI models.

Fortune contacted 2077AI seeking comment about the purpose of the procurement request and whether the books were intended for AI training. The company did not respond to requests for comment before publication.