V1 has two parts. It is the highest speed from which you can reject the TO and stay on the pavement and also the lowest speed you lose an engine, continue the TO, and meet the 35 foot (on a dry runway) screen height. It was redefined several years ago from being the "TO decision speed" to being the speed at which the first action of the rejection takes place. Which means the decision occurred earlier. Which means the event which triggered the decision occurred even earlier. Depending on the aircraft there is at least one second between Vef and V1 for this decision to take place.
Interesting reading-
https://www.faa.gov/other_visit/avia...off_safety.pdf