He accelerates out of the starting blocks at 9.5 meters per second squared, which amounts to nearly 1 g, (0.97 g). The Physics of Usain Bolt's World Record 100-meter Dash. At the end of the race when he pulls ahead of all the other runners, he actually is running more than a kilometer per hour slower than he was at 80 meters. And the other 100 meter sprinters slow down too, by similar amounts, at the end of the race. It is just that after slowing down he is still faster than any of the other 100 meter runners. This is an analysis of his 9.58 seconds run.

Analysis of Bolt’s 9.58 WR | The Science of Sport

And a more detailed one here:

He hit his peak speed at 50 meters and maintained it all the way to 80 meters. See Beijing 2008: Men 100m race analysis | The Science of Sport

So, though he seems to be running faster towards the end of the race, because he draws ahead of all the other runners in the race, it’s actually that the other runners are all getting tired and slowing down and he keeps going and doesn’t slow down so much.