"I was really hoping that it would get done before [the start of the regular season]," Smith said. "I didn't want to go into the regular season with that. As much as you don't think about those types of things consciously, subconsciously you can't help it. They sit in the back of your head, and you're thinking, 'Oh, I'm playing for a contract,' and this and that. Sometimes it can just be an added distraction. I certainly was hoping and I'm really happy that it did get done."
Smith indicated the delay in reaching a deal was just about finding a number that worked for both sides.
"For me, it was about something fair both ways," he said. "As a quarterback, you certainly don't want to hamstring your team in any way because -- I know this more than anyone -- you rely so heavily on those playmakers around you.
"You certainly don't want to do anything like that, but at the same time, you do want something that's fair. It's tough, trying to find out what that is. Everybody is different. You look at the market and quarterbacks and this and that, but everybody is different, every situation is different. There is a lot that goes into it and I think that's why it did take a little while, but hopefully we got it right."
ESPN and various media reports have the extension worth about $68 million.
Chiefs general manager John Dorsey said getting an agreement done before the start of the season was also his goal.
"This has been a long process," Dorsey said. "You know, [Smith's agent] Tom Condon is very professional in his approach. We had ongoing discussions, consistent discussions, and I'm just glad we can concentrate on football. I'm happy for Alex, happy for the organization."
The Associated Press contributed to this report.