Reid did not respond to inquiries regarding the development, as the Chiefs enter Sunday having lost five of six games after a 5-0 start. A team spokesman claimed to have no knowledge of the change.
It would not be the first time in Reid's coaching career that has he has occasionally turned over playcalling to a coordinator. He did so with Marty Mornhinweg and Brad Childress in Philadelphia and with Doug Pederson in Kansas City, though the sources said Reid will continue to have strong oversight during the game.
Pederson scripted the first 15 plays a couple of times but did not have a genuine start-to-finish playcalling experience. Nagy will be doing more Sunday, sources told ESPN.
Reid also has given strong vocal support to quarterback Alex Smith, but the same team sources say Smith will be on a shorter leash based upon his performance against the Jets.
Rookie top draft pick Patrick Mahomes is the backup quarterback, but the organizational plans have been for him to sit this season before Smith is put on the trade market in the offseason.
The playcalling switch has paid immediate dividends as Smith has thrown touchdown passes on each of the Chiefs' first two drives in the first quarter Sunday with both scoring passes going to star tight end Travis Kelce.