"We're proud of Kris. He's had an unbelievable start to his first full professional season, and he had accomplished a lot of the developmental goals we set out for him at Double-A," Epstein said. "We felt like a promotion to Triple-A to continue to challenge him would be good for him in the long run.
"He still has some things to work on. He'll continue to work on them at Triple-A, but seeing some more advanced pitching, some guys that can execute on a more consistent basis, try to find his holes, change speeds -- it'll be good for him. It's the next step in his development."
Should Bryant continue to excel, the next stop is the big leagues. But Epstein reiterated the Cubs don't plan to call him up this year.
"I don't think it's the right thing to do in someone's first full professional season, barring extraordinary circumstances both to the player and what's going on with the big league club," Epstein said. "I think it would be a tremendous accomplishment to dominate Double-A the way he did the first half of the season and go to Triple-A and continue his development, stay healthy all year and be productive all year and continue to work on his weaknesses."
Relievers Arodys Vizcaino and Armando Rivero were also promoted to Iowa.
Vizcaino threw 17 1/3 innings for the Braves in 2011 and was a key piece in the Paul Maholm deal that summer. He missed all of 2012 due to Tommy John surgery and all of '13 due to calcium buildup in his elbow, but the 23-year-old seems to have regained his stuff. The righty, who has been consistently reaching 98 mph on the radar gun, posted a 1.99 ERA with 26 strikeouts in 22 2/3 innings at Class A Advanced Daytona and Double-A Tennessee this season.
"With Vizcaino, it's really just healthy and continuing to be consistent with his mechanics and throw that breaking ball. I think he's been kind of using it more and more lately and getting a lot of swings and misses with it," Epstein said. "So using all his pitches, getting in different game situations -- he's a big league pitcher, he's been up before, it's really just a matter of sort of getting back in the routine, feeling comfortable after the surgery, and then he'll be up here."
Rivero was impressive at Tennessee as well this season. He posted a 1.56 ERA and a 0.98 WHIP in 34 2/3 innings, while striking out a whopping 54 batters in 34 2/3 innings.
"I think with Rivero, it's really fastball command. He's got really good stuff, and when he's locating his fastball, consistently getting ahead and finishing guys off with his slider, it's really impressive punching out a ton of guys," Epstein said. "The better hitters there will force him to be more locked in and continue to work on that fastball command."
Cubs manager Rick Renteria said he's well aware of what Bryant and other impressive prospects are doing.
"But I am more concerned with the guys that are here right now. I have to be," he said. "I think the biggest thing that we watch for is I have to really concern my focus on making sure I'm reading these guys well and understanding what's going on with them. On the periphery, obviously we're aware of everything that's going on."