Great question Sebastiaan!
The answer is that it depends on the distance of the race. Your peak weeks are typically 3 weeks out. You will decrease the volume typically across the board (and your volume has decreased even if it’s still 12+ hours per week). However, depending on the distance that you are training for, what we need to do is prime your ‘race specific’ HR. So for shorter course races, you decrease the volume and increase the intensity (short but fast) to prime your high end threshold. You will do some of this same type of effort for the Half Ironman distance too. For the Ironman distance, your high end threshold is not as important. However we still want to make sure we keep your lactate threshold high and trained. So we still do some short but sweet intervals to maintain your conditioning.
During taper for the IM distance, you often see some more race specific swim workouts. Because swimming is more recovery like and this is the first sport that you will start to lose fitness (because it’s so technique based), for the IM distance, you will see longer swim workouts remain for the next week or so.
In the end, you are supposed to focus on strengthening, foam rolling, sleeping, eating well and completing your race plan. Thankfully you have a few extra hours now to allow you to prioritize these things!