Purdue coaches have shown interest in the younger Thompson for the better part of his high school career to this point and watched him particularly closely this past spring and summer.
"I think I saw it coming a little bit," Thompson said. "I've been talking to Coach Brandon (Brantley) and Coach (Matt) Painter since the summer and it's been pretty heavy, them recruiting me pretty heavy. They just talked about wanting to establish their 2018 class, then move on to 2019."
Thompson's offer came on the heels of Purdue landing guard Eric Hunter as its third Class of 2018 commitment, the possibility being now that it could stand pat with those three recruits for the early signing period.
"They wanted to let the 2018 class play out," Thompson said, "but I always knew they really liked my game a lot and they'd recruited me pretty hard, so I kind of expected it, but it's still surprising and really exciting."
The 5-foot-11ish Thompson averaged about 18-and-a-half points for Zionsville as a sophomore, prior to a big summer in which he hit for 41 in a game in July at the 16-and-under Peach Jam.
"They like how I'm a point guard but I can also play off the ball," Thompson said. "They've seen how players like Carsen Edwards can play the 1 but also play the 2, and sometimes my better play might be off the ball, too. They like that, how I can play the point or play off the ball and really score, but also distribute the ball to my teammates also."
Thompson had previously been offered by Miami (Ohio) — its head coach, Jack Owens, had long recruited him for Purdue and has known Thompson's family for years — Toledo, Kent State and IUPUI. He's fielded early interest as well from Butler, Xavier, Iowa, Nebraska and others.
"I'm still open, but I'm really excited about the offer," Thompson said. "I am really open to anyone, but am looking forward to the recruiting process with Purdue and any other school, but I really like Purdue a lot. I've been there so many times, I'm so familiar with things, and getting this offer tonight was very exciting for me and my family."
Thompson said he plans to visit Xavier, Butler and Miami (Ohio) in the weeks to come.
He's seen about as much as possible of Purdue to this point.
Because of P.J. Thompson's presence in West Lafayette, Isaiah Thompson's been a regular at Purdue, both for games in the winter, football weekends in the fall and whatever else in between.
"When I'm down there with the guys — and (P.J. Thompson) has told me this, too — they're all so together," Isaiah Thompson said. "They're like a big family and that's something I know that when I pick a college is going to be important: How together a team is."