Marvel Cinematic Universe fans expecting an extended cut of Avengers: Infinity War on home video that re-adds over 30 minutes of footage detailing Thanos' backstory may want to stop holding their breath.
Josh Brolin's Thanos has been widely and repeatedly cited as one of the strongest aspects of Avengers: Infinity War; despite being a CGI foe with magical MacGuffin goals - something that has waylaid both Marvel and DC in recent years - the Russo brothers were able to imbue the role with real empathy, ironically without ever showing a tragic past which in the comics looms large. Unsurprisingly, rumors that the Mad Titan's absent origins are being reinserted - the latest MCU news suggests Thanos creator Jim Starlin has claimed it's part of an extended Blu-ray cut - has been very positively received.
Some have immediately raised issues with the suggestion given that the already-announced extras for the Avengers: Infinity War Blu-ray include just three, short deleted scenes, none of which are linked to Thanos. However, in their report, Collider did make clear that any extended version wouldn't be in the initial home video release, but at a later point.
Marvel Don't Seem To Have Finished Thanos' Backstory
Even then, though, there's reason to doubt this development. Various creatives involved in Avengers: Infinity War have discussed how there was a fleshed out flashback sequence for Thanos in the script that detailed his childhood and what drove him to believe destroying half of all life was the only way to save the universe - but that it was never created. When Screen Rant talked to VFX supervisor Matt Aitken of Weta Digital about his work on the Titan sequence, he said that assets - including other, different-looking Titans - were made but the studio never went as far as developing the scenes:
"Originally there had early on been a longer sequence that we were going to be involved in that was a longer flashback to the original Titan, which explained in more depth Thanos' motivations and what's driving him, but they ended up boiling it down to [what's in the movie]... It's essentially telling the same message but in a more concise format, with this more handful of shots."
This is the best evidence we have that the sequences don't exist in any usable form.
Indeed, the Russo brothers have stated the released Avengers: Infinity War isn't too different in length to their original director's cut, indicating if anything on Thanos' past was done, it was removed before completion. What seems more likely, then, is that early storyboards or even scripting for these sequences were shown to Starlin then removed earlier in the development process than the originating report suggests.
Marvel Don't Really Release Extended Cuts
The recent rise of extended versions of tentpole movies - most famously the 30-minute longer Batman v Superman: Dawn of Justice - Ultimate Edition which reinserted key secondary subplot information - has made the possibility of an alternate version of Avengers: Infinity War feel more likely. However, we know this isn't something Marvel has real intentions of going in for; when Screen Rant caught up with producer Nate Moore, he said Marvel Studios doesn't just have few deleted scenes due to unfinished visual effects, but that they're reluctant to release longer cuts to avoid confusing canon or wasting good ideas that could be used further down the line:
"If there are ideas or scenes or notions that could work in other films that maybe were in this cut, what we want to do is save them for a rainy day because you never know when a great scene or a great idea can be used in another film. So sometimes there are things we'll never show audiences because we know we can repurpose them in another film."
The only evidence for there being 30 minutes of unused-yet-completed footage of Thanos from Avengers: Infinity War, let alone it existing in a re-edited version of the finished film, comes from second-hand information, while everything else suggests otherwise. However, if Marvel is wanting to not use up an idea, it's not out of the question for us to see this used in some form in Avengers 4.