It’s not every day that a Magic set adds a new subtype, but Secrets of Strixhaven is doing just that. From this expansion on, Book will be an official artifact subtype for the game, representing the various tomes and grimoires of the multiverse. While Secrets of Strixhaven itself only contains one new Book, 45 older MTG cards are receiving the type via errata.
The MTG Secrets Of Strixhaven Book Errata

This change was promised in the official Secrets of Strixhaven mechanics article, but it took until now to come to fruition. Even now, the update hasn’t exactly been made official. It was only via trawling Gatherer that MTG players discovered that 46 MTG cards have been errata-ed into Books.
Currently, it’s unclear if Wizards is planning anything with this change, such as future Book Typal cards. Technically, this is a possibility, but realistically, a new card type and errata aren’t a promise of future support. Since the Sorcerer type returned to MTG alongside a 30-card errata, for instance, no Sorcerer Typal-focused cards have been released.
With this in mind, Wizards may simply be making old books into Books, now that they’ve allowed that artifact type. Whether or not this is actually the case, however, remains to be seen, as Wizards hasn’t explained their reasoning just yet. For now, here’s the full list of all 44 MTG cards that have received the Book subtype in this new errata.
In addition to these full-card erratas, tokens produced by the following three cards will also be classified as Books:
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