-Reay will recognize his IndyCar championship next season by using the No. 1 on his Andretti Autosport entry.
Hunter-Reay becomes the first defending series champion to follow the open-wheel tradition of using the No. 1 since Scott Dixon switched numbers following his 2003 IndyCar title. Dixon did not switch numbers after his 2008 championship.
Hunter-Reay had been using the No. 28 to recognize the estimated 28 million people living with cancer, and created awareness to the cause through his Racing for Cancer organization. But he felt switching to No. 1 would properly credit Andretti Autosport and his sponsors for their 2012 championship.
"The decision to switch to the No. 1 for the 2013 season was very tough. The No. 28 has so much meaning to so many," he said. "But we recognized that our team, partners and sponsors have all earned the right to carry the No. 1. We worked hard together and it's something they all deserve."
Hunter-Reay's original number will still be part of the car design, which will have DHL as the sole primary sponsor under a multi-year agreement announced Wednesday. DHL had previously shared the primary sponsorship role.
"Racing for Cancer's number one goal is to beat cancer and we realized that running the No. 1 with the No. 28 incorporated into the design, a very important detail to me personally, would provide us with an opportunity to strengthen the message and cause of beating cancer while at the same time recognizing our partners and sponsors dedication to excellence on, and off, the track." he said.
Hunter-Reay became the first American since Sam Hornish Jr. in 2006 to win the IndyCar championship last season when he upset Will Power to win his first title. He won three consecutive races during the summer to pull into championship contention, then won at Baltimore in September to climb back into the race when Power was on the verge of clinching.
Also changing numbers in the Andretti stable next year is Marco Andretti, who after seven seasons using No. 26 decided the number is unlucky and will drop down a digit to No. 25.
"The No. 26 will always be a part of me and my history in racing but I think it's grown unlucky for me," he said. "I keep hearing that from people too. I like the meaning of 25 versus 26. To me 26 is a character builder through heartache and trials and looking ahead to the No. 25 means success and leadership. It's like my chance to be reborn as a veteran driver."
James Hinchcliffe will keep his No. 27 as he enters his second season with Andretti Autosport. But, it's his first time returning with the same team for consecutive seasons.
"For me, personally, this is the first time in my career I'll have the same team for two years in a row ... have the same crew and not have the learning curve at the beginning of next season," said Hinchcliffe. "I won't have a new situation and a new team to learn and settle into and I'll have the same two teammates which great - it's just good to know that off the bat we'll be able to move forward."
Paul Tracy used the No. 1 in Champ Car following his 2003 championship, and Sebastien Bourdais used it following his 2004-06 Champ Car titles.