No, Adam Warlock ISN'T In Avengers 4
Please, stop asking.
No matter how many times James Gunn has said there's no way Adam Warlock will be appearing anywhere outside of Guardians Of The Galaxy Vol 3, there's still been some speculation that we might get to see the hugely powerful anti-hero turned hero appear in the Infinity Saga movies. After all, he was a key element in the comics and it would fit.
Well, it would fit if you ignored the fact that the Russos and their writing team had completely changed almost everything about the Infinity Gauntlet story (and the other comics the movie was based on). But that appears to be what a number of commenters are doing at the minute by still wondering whether Warlock will appear in Avengers 4.
The fact that the Soulworld was introduced at the end of Infinity War could definitely be used as an in for the character to appear. It is - after all - the realm that Warlock is trapped in in the comics when he encounters the Silver Surfer and learns of Thanos' conquest. But it wouldn't make any sense for him to appear.
That's why the Russos have once more reiterated the fact that he won't be appearing in Avengers 4 (while in conversation with ComicBook):
“Yeah [Adam Warlock]’s not showing up in our stories. Look, our job as we said a million times is to tell the story of the Marvel Cinematic Universe, not to do direct adaptations of the comics because we’re comic book fans. I have no interest as a director in telling a story that’s already been told or in seeing one that’s already been told. If I know all the events story as they’re going to happen then what’s the point of going to the film? We want to keep surprising audiences and continue the story that started with Iron Man […] a decade ago.”
Advertisement
Why does need saying? Warlock is literally going to be the villain (at least initially) in Guardians Vol 3 after we saw him created by Ayesha in the preceding movie as a weapon against the Guardians. Sure, he'll probably have his moment of heroic revelation as he did in the comics, but he needs all of that backstory to happen before he just suddenly appears in the MCU.
Dropping him into Infinity War's sequel without establishing him properly would undo that key seeding scene in Vol 2 and Marvel have done that more than enough times to know it's not the right approach. So stop asking about him, yeah?