Diana Gabaldon has started writing Book 10!
Here's an exciting bit of news from Diana Gabaldon, posted on her Facebook page on September 25:
Oh--and I started work on Book Ten yesterday....
This is great news! I honestly wasn't expecting her to dive right back into the next Big Book only a few weeks after she finished the last of the revisions to BEES, but it's good to hear that she's started, at least.
As far as we know right now, Book 10 is expected to be the last in the main OUTLANDER series. But that's not written in stone! Diana doesn't plan the books out in advance, and she likely won't know for sure whether it is indeed the last one until she gets pretty far into the writing.
Also keep in mind that it took seven years for BEES to be completed, so it might be that long before we see Book 10. If it is indeed going to be the last book in the main series, I think I personally could wait forever.