The Northamptonshire track offers free admission to racegoers and is expecting a bumper crowd, with the possibility of sporting history being made.
As my old friend the BBC racing correspondent,Cornelius Lysaght, puts it:
"While 4,000 sounds colossal, it really is - nearly 1,500 successes more than any other rider over jumps. Once upon a time to get to 'a mere' 1,000 was considered something very special. To an extent, as there's no question of him getting to the milestone and then abruptly retiring, this is just a number, but when you get to such a landmark, whether it be in sport or business or marriage, it's a good time to celebrate.
I dare say McCoy himself would like to just get on with riding minus any hype, but racing is understandably keen to shout about one of its own who is unquestionably one of Britain's most extraordinary sportspeople.
Nearly 4,000 winners and 18 champion jockeys' titles over nearly two decades in - and this is crucial - the most perilous of sports where you 'play' not only with animals, but followed around by an ambulance, is indeed a colossal achievement."
For my part I am lucky to have known, followed and admired AP - he is a genuinely great man, and a supreme horseman. We will never see the like of him again. I wish him well today.
UPDATE: AP does it! Great news that he won at Towcester today
http://www.bbc.co.uk/sport/0/horse-racing/24850985
