Yom Kippur shaḥarit is prayed as per usual. And it is customary to say the Song of Unity for that day, and An'im Zemirot, and the psalm of the day, before prayer. And the blessing "who has made for me all my needs" is not said. And the Rosh, the Ran, and the Tur (§ 613) disagree on this — see therein. And each person can do as he wishes, but from the Rambam it appears that it is not blessed. And the piyyuṭim are all according to custom. But what astonishes me is that the Rosh on Yoma, and the Tur in said section, brought down in the names of the gaonim to say the Thirteen Attributes five times in shaḥarit, and some say thirteen times to correspond with the thirteen attributes, and some say seven times, and in musaf seven times, and so too in minḥa — see therein — but we don't mention it even once! And there are baseless customs which we are careful to follow, but to say the thirteen attributes — that which is from the gaonim! — we are not careful. (And all this sprouted from the lengthening of melodies, until there was no longer time to say seliḥot. And saying the thirteen attributes is impossible without saying seliḥot. And the great gaonim have already decried the cantors, but we have no power to protest, may God forgive!)

The Tur and the Shulḥan Arukh wrote that it is proper to shorten the shaḥarit piyyuṭim, so as to pray musaf before the seventh hour, lest the time for minḥa arrive and they be forced to advance it, as I wrote in § 286. And the Tur and the Rosh wrote that when one sees that the community is lengthening shaḥarit one prays musaf alone — see therein. And we are a priori careful about this, but post facto there is no concern, for many disagree about this, as I wrote therein. And specifically, some say that this is just on account of eating, as it is forbidden to eat when the time for minḥa arrives, as I wrote there, and this is irrelevant on Yom Kippur. (And the Magen Avraham brings that the Mahari"l, when shaḥarit went late, would not say Avinu Malkenu.)