Google has been quietly slowing down its book-scanning work with partner libraries, according to librarians involved with the vast Google Books digitization project. But what that means for the company's long-term investment in the work remains unclear.

Google was not willing to say much about its plans. "We've digitized more than 20 million books to date and continue to scan books with our library partners," a Google spokeswoman told The Chronicle in an e-mailed statement.

Librarians at several of Google's partner institutions, including the University of Michigan and the University of Wisconsin systems, confirmed that the pace has slowed. "They're still scanning. They're scanning at a lower rate than the peak," said Paul N. Courant, Michigan's dean of libraries....