Gloucester-born Stevens, 20, was recalled from League One side Swindon Town, for whom he scored one goal in 15 games in the first part of the season.
He has been limited to just six first-team matches for his parent club since joining from Forest Green in 2018.
"It is a very big club," Stevens said of the move to Valley Parade.
"I am looking forward to meeting up with the rest of the lads. I have played in this division before and have picked up a fair bit of experience at Swindon Town this season, so am excited for the challenge."
Interim manager Mark Trueman added: "He is a very talented player - with raw pace and a naturally direct edge to his play - and we are looking forward to seeing him in action."