PrimeWire

Back in June of ‘22 this was published on “Collider” . . .

“According to Variety, the show has been given an extended renewal for Seasons 3 and 4, and all we’ve seen so far is a debut season that ran for six episodes. Based on the books by Mick Herron, Slow Horses had initially been given a two-season order. The double-season renewal is a sign of great confidence in the show, and perhaps an overeager move to lock down the services of its Oscar-winning star, Gary Oldman.”
“In the third season, Lamb’s disgraced spies must work together when one of their own is kidnapped, while a rogue agent is on the loose. The fourth season reportedly deals with a bombing that threatens to rock the very foundations of Slough House. Saul Metzstein is set to direct the third season, though no director for the fourth season has been announced. James Hawes directed Season 1, and Jeremy Lovering directs the second season premiering later this year. “

. . . from what I’ve been able to glean from the net, this has held true. Seasons 3 & 4 were shot back to back and Oldman stars in both. Perhaps there’s contradictory information out there that I haven’t seen but I sure hope not as this is SUCH a very GOOD show.