4 x 8 with 2 min recovery.
The work bout is done at the ‘maximal sustained effort’. The study cohort was male cyclists. Here is the reference:
That simple description of ‘max sustained’ was then boiled down to 4 x 8 at 105-110% FTP as a starting guide because most folks seem to want a power number target not an RPE or self paced target.
In reviews of recovery periods for different sports, 1 min between longer intervals (4-8 min for discussion) was not enough. 2 min was sufficient and longer is probably not needed physiologically.
FWIW, having tried 4 x 8 at 105% with 2, 4 and 8 min rests, the 2 was not enough for me, 4 was OK on good days, 8 was a bit too long (4:1, 2:1, 1:1 ratios).
Seiler has a nice compilation of information around rest periods in a review available at Research Gate. It is a PDF from July 2017. This link will probably break but y’all can apply some Google and find it quickly.