Spider-Man: Into the Spider-Verse spoilers ahead. There are a lot of Spider-People in Spider-Man: Into the Spider-Verse, and in the post-credits scene we get to check out yet another one. And if you think his voice sounds familiar, that's because Oscar Isaac has an Into the Spider-Verse cameo in which he plays that post-credits Spider-Man. He only has a couple of lines, but his brief appearance could be a sign of more to come.
Into the Spider-Verse is all about different Spider-People from different realities coming together in Miles Morales' world. They fight bad guys, they have emotional moments of bonding, they learn about each others' origin stories. Then, at the end of the movie, the various Spider-People all go back to their respective realities. But, in the post-credits scene we see that the inter-dimensional travel is not over.
In the post-credits scene, a version of Spider-Man named Miguel, who has a different costume than the "normal" Spider-Men, shows up along with text reading, "Meanwhile in Nueva York." According to ComicBookMovie.com, Miguel's talking to his assistant Lyla (Greta Lee), and he says, "Let's go back to the beginning on more time." With this, he travels to Earth-67, sees another Spider-Man, and they do their take on that Spider-Man Pointing at Spider-Man meme. The end.
If you aren't familiar with Miguel, here's the deal: he's Spider-Man 2099, a Spider-Man who lives in the year 2099. (Hey, these numbers can get confusing. There are a lot of Spider-People and Spider-People realities.) As explained by Comic Vine, in the comics, Miguel worked at Alchemax — which is the corporation that is responsible for the realities intertwining in Into the Spider-Verse — before he gained his powers. This explains why in the post-credits scene he has the means of traveling to another dimension.
Of course, with any post-credits scene, the whole point can be to hint at what's to come in the next movie. Many of the movies featuring Marvel characters (like Avengers) are produced by Marvel and distributed by Walt Disney Pictures. But, Sony shares the rights to Spider-Man and has plans for more movies in addition to Into the Spider-Verse and the Tom Holland series of Spider-Man live-action films, the latter of which are both distributed by Sony and part of the Marvel Cinematic Universe. (For a more in-depth rundown of all of these studio and production connections, check out this explainer from Collider.) For now, according to The Hollywood Reporter, Sony is planning an Into the Spider-Verse sequel and a spinoff movie all about female Spidey heroes.
Because a sequel is reportedly on the way, Isaac could be coming back to voice Spider-Man 2099 again for that. Perhaps he'll meet up with Miles Morales and the rest of the gang, or maybe it'll just focus on him. Either way, the post-credits scene seems like it's setting up some sort of return for Spider-Man 2099.
For now, none of this has been commented on by the studio or by Isaac. The scene is meant to be a total surprise, and Isaac and Lee are still listed on the Spider-Verse IMDb page as Interesting Person #1 and Interesting Person #2. Can't say that's not accurate.