The San Francisco 49ers made a roster move on Wednesday, placing linebacker Blake Costanzo on injured reserve, and signing linebacker Kion Wilson. There is no word on Costanzo's injury, but it either happened during last Thursday's game, or during one of the joint practices, because he first indicated he was signing on Sunday, August 10. Costanzo was a vested veteran, and thus did not have to clear waivers through the waived/injured designation.
Costanzo was competing for a special teams role, and the end of his season opens the door for some other special teamers. It does not have a ton of bearing on the linebacker competition because Costanzo would never play inebacker during the regular season. On the other hand, maybe the team looks linebacker for that special teams role just to have that depth option in case of emergency.
Wilson entered the NFL in 2010 as an undrafted free agent. He signed with the San Diego Chargers, and appeared in 3 games with the Chargers, spending additional time on their practice squad. He started the 2011 season on the Chargers practice squad, and then signed to the Carolina Panthers active roster on November 16, 2011. The Panthers waived him following training camp in 2012. He signed with the Pittsburgh Steelers in 2013, and spent time on the team's active roster and practice squad that year, registering nine tackles in seven games (two starts) for the Steelers.
Wilson went to South Florida, so this reunites him with 49ers linebacker coach Jim Leavitt, who previously was the head coach at USF. Here is an old scouting report, and here is a feature article shortly after he signed with the Chargers.