Sony knew Into the Spider-verse would be a hit. Prior to the film's December 14 premiere and near-perfect Rotten Tomatoes score, the studio had already announced a sequel and a spinoff were in development. The sequel will likely expand on the Into the Spider-verse post-credits scene, which we'll get into below. The spinoff will follow the women of the Spider-verse, and the Into the Spider-verse ending offered some clues for that film too.

Into the Spider-verse introduced Marvel's multiverse, and the post-credits scene expands that universe even further. The scene introduces Miguel O'Hara, a.k.a. Spider-Man 2099, who possesses a watch that can transport him across realities. It drops him in the 1960's Spider-Man animated series universe (yup, the one which spawned that meme of the two Spideys pointing at each other). Behind the humor is a huge hint for the upcoming sequel and spinoff movies. Into the Spider-verse saw the spider-people stop Wilson Fisk's particle collider from destroying the multiverse and all the spider heroes returned to their respective universes, leaving Miles all alone. Now, we know that multiverse-hopping is possible. Miles can indeed visit his friends once again, and this opens of a slew of possible new adventures for this franchise. It also sheds light on the film's actual ending.

Miles falls asleep in his bed after his stressful first week of being Spidey. He saved the world once, but he's going to have to save it again… and sooner than the thought. As he dozes off, Gwen's in his head. "Got a minute?" she asks. Since Gwen helped out Miles on his Earth, it's only right Miles returns the favor.
Perhaps this is the beginning of Gwen's story in the spinoff film, where she'll (hopefully) be joined by other female Spidey heroes like Spider-Woman, Spider-Girl, Madame Web and Silk. It also proves Gwen has found a way to communicate with Miles, again nailing home the idea that we're going to see Spidey people from different universes team up again. But which film will come first… the sequel or the spinoff? Whichever releases first will have to establish this new Earth-hopping tech.

Spider-Man 2099's last-minute appearance does have some more clues, hidden in the pages of Marvel comics where Miguel is a geneticist tasked with making a drug that replicates Peter Parker's Spidey powers. Long story short, a few things go awry in the lab, and he ends up with Spidey DNA. It's also worth noting the spider that gave Miles his powers in the flim appeared to glitch, just like the other spider-people who belonged to different universes. Could this be a hint that the Spider who bit Miles is somehow related to the work of geneticist Spider-Man 2099?

Spider-Geddon is another comic storyline relevant to both the appearance of Spider-Man 2099 and the impending Into the Spider-verse sequel. Into the Spider-verse was an adaptation of Spider-verse, a 2014 storyline featuring multiple alternative versions of Spider-Man, just like the film. 2018's Spider-Geddon was the sequel to that arc. In it, Miles and his team of Spider people fight off a group of villains called Inheritors, who feed on people with Spidey powers. It's anyone's guess whether the sequel will take inspiration from Spider-Geddon, but you don't cast a big name like Oscar Isaac as Spidey 2099 for no reason.
Any theories about the sequel or spinoff? Sound off in the comments.