It's mainly iteration length that has shortened. Royce was saying do it twice (including requirements engineering, which presumably would involve some kind of feedback). Spiral development increased that to doing it multiple times. Rational unified suggested a quarterly pace. Most agile methodologies work with sprints of a few weeks.
And lately, continuous deployment and Kanban like methods remove iterations completely and release continuously. Ship when ready and develop asynchronously. You can still have planning cycles with this of course but they are decoupled from release cycles.
The Linux kernel is a good example where you either make the merge window or wait for the next one. Large companies like Meta are also know to work with scheduled releases that are independent from planning cycles (e.g. weekly) of teams.
And lately, continuous deployment and Kanban like methods remove iterations completely and release continuously. Ship when ready and develop asynchronously. You can still have planning cycles with this of course but they are decoupled from release cycles.
The Linux kernel is a good example where you either make the merge window or wait for the next one. Large companies like Meta are also know to work with scheduled releases that are independent from planning cycles (e.g. weekly) of teams.