To add some color here: It is very helpful to have someone pace you so that you can run an ideal pace without worrying about whether you are running the right speed. However, the rules require that pacers start with you [0], which means that by definition if you are running faster than anyone has ever gone before you have to run some of the race alone.

However, because marathon are often mixed gender and the best male runners are significantly faster than the best female runners, it is possible for a woman to be paced from the gun to the tape by a male runner. For this reason, there are separate records for the women's marathon for women's only events.

[0] This is one of the things that made Kipchoge's original sub 2 result not record-eligible.