They're only legal if training is fair use - and even I don't think it's immediately clear what would be the legal status of verbatim regurgitation of code in copyright, or code protected by patents?
AFAIK I (as a human developer) can't assume that I can go and copy code out of a text book, and then assume copyright and charge for a license to it?
The judge seems to have said it's because they "transformed" the books (destroying them after digitalizing) in the process, that made it legal.
> Ultimately, Judge William Alsup ruled that this destructive scanning operation qualified as fair use—but only because Anthropic had legally purchased the books first, destroyed each print copy after scanning, and kept the digital files internally rather than distributing them. The judge compared the process to “conserv[ing] space” through format conversion and found it transformative. - https://arstechnica.com/ai/2025/06/anthropic-destroyed-milli...