They made a vague promise a long time ago that they will "endevour to publish one monthly".
Our strategy from day one has been to continuously and transparently develop our most important asset Sailfish OS. In just over half a year we have pushed out seven big software updates, bringing new features and fixes to the user experience, on a monthly basis. We are continuing this strategy, i.e. we like to say that your Jolla smartphone gets better every month, and at the end of this year it will not be same as it is now. So in this sense, Jolla smartphone is never outdated or old.