It’s becoming increasingly rare for a scripted series to make it to its fourth season in the streaming era. The bean counters and data crunchers have divined that the fresh subscribers a show can bring to a platform have been exhausted after three seasons, so it’s better to put the production budget into a new title and start the cycle once more. Mercantile to the point of mercenary, this outlook gets shows, at best, wrapped up, or simply cancelled.

Given those cold calculations, we should absolutely celebrate two shows that are currently not only airing their fourth season via weekly episodes, they’re flourishing while they build a lasting body of work. Defying both expectations and their genres, Apple TV+’s Slow Horses and Disney+’s Only Murders in the Building are television’s four-to-the-floor series. The British espionage thriller and the American murder-mystery comedy are a reminder that a great series can get even better when it finds its groove.

What do the shows have in common? For a start, each was a smart bet that the star of their ensemble was being put in a role that was right in their wheelhouse. Gary Oldman’s Jackson Lamb, the sardonic spy master of Slow Horses, is a cholesterol test’s worst nightmare who emits strange odours and dismissive quips. His gut instinct is considerable in worryingly different ways. “Bringing you up to speed is like trying to explain Norway to a dog” is a typical kiss-off.

In Only Murders in the Building, a show he co-created, Steve Martin is a goofy but nonetheless egocentric delight as Charles-Haden Savage, a former TV cop show star from the 1990s whose efforts to be cool or considered are often sidetracked by a narcissistic streak that is more amusing than problematic. But Charles is a more than OK Boomer. Seeing him come alive in the company of unlikely new pals and true crime podcasters Mabel Mora (Selena Gomez) and Oliver Putnam (Martin Short) is a genuine delight.

Both shows also work their way around a season-long case: a threat to national security for Slow Horses and a homicide with quirky clues in the Manhattan apartment building where Only Murders is set. By rights, they should be getting repetitive, but there’s a thoughtfulness in the writing – overseen by Will Smith (Veep) on the former and John Hoffman (Grace and Frankie) the latter – that provides genuine nuance and surprising twists. The passing of time has added welcome wrinkles.

For example, on the current season of Only Murders, the podcasting trio’s fame has gotten to the point where Hollywood’s Paramount Pictures wants to adapt their story, complete with a famous cast: Eugene Levy, Eva Longoria, and Zach Galifianakis play eccentric versions of themselves cast as Charles, Mabel, and Oliver respectively. It’s so silly and self-referential, but it’s consistently funny – “Please don’t ever touch my murder board,” Mabel tells Longoria – and quietly knowing. Seeing how the actors view them makes the trio reconsider who they are.

Both shows have always been confident in their respective outlooks. When the first season of Slow Horses reached a finale, Lamb and his team of MI5 misfits, the “slow horses” kept hidden away at decrepit Slough House, raced to intercept a far-right nationalist and his hostage. When they got to the target’s location, the agents ran towards the trouble but Lamb, who definitely does not run, simply sat down in a carpark and lit up a cigarette. The show didn’t need Oldman present to vindicate a life-or-death conclusion, and it worked.