So after that panel last summer, Shannon Messenger confirmed 'Stellarlune' was the end of Book 8's arc, and she'd be taking a longer break before diving into Book 9's main plot. There's been no official announcement for a date yet, but looking at the usual timeline, we're probably still a ways out. She just started drafting it a few months back, and between writing, editing, and the whole publishing machine, it takes over a year, sometimes closer to two.
I keep checking her Instagram for any hints, but she's mostly sharing cute dog pics and process stuff. My guess is we won't see it before late 2025 at the absolute earliest, maybe even 2026. It's a bummer, but honestly, after the intensity of Book 8, I'm glad she's giving herself time to make sure the next one lands right.