I tried tracking this for a while when I was catching up, but the schedule's honestly more of a vague suggestion than a strict timetable. The author seems to publish in big, meaty chunks, not little weekly drips. I went through the first four volumes last year, and there was a solid eight-month gap between book three and book four, but then book five showed up only about five months later. It feels like they work in bursts – a flurry of activity, then radio silence while they build up the next big story arc.
Some readers on the series forum get antsy during the quiet periods, but I kinda prefer it. The installments are usually 500+ pages, and you need time to sit with the dense world-building and political machinations. If they came out monthly, the quality would probably tank, or I'd just fall hopelessly behind. The waiting makes the actual release feel like an event. I just wish the author's blog or the publisher's page would give a heads-up more than a month in advance; finding out a new one is up for pre-order always feels like a surprise birthday present.
So, to actually answer, it's irregular but averages out to maybe two a year? Don't quote me on that. The pattern is 'when it's ready,' which I can respect, even if it means my reading list gets rearranged whenever a notification finally pops up.