The next entry in The Witcher book series is done being written, says the author himself, Andrzej Sapkowski.
Sapkowski casually revealed the news in an interview with Chimères (thanks, Culture Crave), saying "it took me two years, something like this" to finish the book. It's still unclear exactly when the as yet-untitled book will actually hit store shelves, but Sapkowski said last August that it wouldn't take more than a year to release, so the clock is definitely ticking on his ability to meet that self-imposed deadline.
If it released today, the book would be the first new Witcher book in 11 years, following 2013's prequel story Season of Storms. The next book will be similar to that one in the sense that it's yet another standalone entry that, while canon with the rest of the series, isn't part of the main Witcher saga. Instead, this one will be focused almost entirely on Geralt.
For most fantasy readers, it's impossible to talk about this news without also mentioning what A Song of Ice and Fire author George RR Martin said today about his own book series. Speaking at the Oxford Writers' House, Martin said the one thing he'd change about his books is that he'd "have them finished," which is of course exactly what fans of the series have desperately wanted since Dance with Dragons released way back in 2011.
Of course, every writer's process is different and despite being two fantasy book series, A Song of Ice and Fire and The Witcher are incomparable in scope, tone, and intent. That won't stop my eyes from rolling out of my head when Martin gives another inevitable 'Winds of Winter still isn't done' update, but it's worth noting.
Meanwhile, The Witcher season 4 production begun in April and Netflix confirmed season 5 will be the show's final season.