It looks like a third Sicario movie is really happening. Denis Villeneuve directed the first movie, with Stefano Sollima taking over for the second. Both were from scripts by Yellowstone supremo Taylor Sheridan.
Rumors first started back in the summer, as The Dog Stars actor Josh Brolin was out doing promo for that movie when he talked about the project. Yesterday, Variety reported that Sheridan has written a script and the project is potentially moving forward.

Other than Brolin returning as Matt Graver, the CIA SAC officer who uses unconventional methods to push back against Mexican drug cartels along the Mexico-United States border, nothing else is known about the sequel, aside from its rumored title: Sicario: Capos.
The previous instalment had final scenes that were open-ended and showed one key character surviving and recruiting. Featuring Gillick and Graver entering Mexico to basically start a war on purpose between the rival Mexican cartels, the second movie has actually been described as more of a “stand-alone spin-off” rather than a sequel or prequel by both Sheridan and the director.
Sheridan also said:
“If Sicario is a film about the militarization of police and that blending over, [Soldado] is removing the policing aspect from it.”
Sheridan is currently writing the script for the upcoming Call of Duty movie, which Peter Berg is set to direct.