
An easy-to-miss detail in the Fantastic Four: First Steps trailer may tease he team's reported dimensional jump into the MCU's Sacred Timeline.
After what feels like an eternity, Marvel's First Family will finally come to the Marvel Cinematic Universe on July 25, 2025.
The Fantastic Four: First Steps introduces Reed Richards, Sue Storm, Ben Grimm, and Johnny Storm into the house that Marvel Studios built and also primes them for their confirmed roles in the next two Avengers films.
Reed’s Chalkboard Could Hold the Key to His Avengers Appearances

At the 39-second mark in Marvel Studios' much-hyped The Fantastic Four: First Steps teaser trailer, Pedro Pascal's Reed Richards (Mister Fantastic) is seen intently marking a chalkboard.
All things considered, this is a typical Reed Richards action, but one detail in particular that he's scrawled on the board stands out.
On Reed's left, a diagram depicting what looks to be an Einstein-Rosen bridge (or, in more casual parlance, a wormhole) can be glimpsed. What's even more interesting is that the endpoint of this wormhole is labeled "another universe."

This schematic confirms one specific thing and heavily hints at another. Firstly, it tells the audience that Reed is researching Multiversal travel and trying to find an actionable means of accomplishing it.
Since all four members of the Fantastic Four (FF) have been confirmed for both Avengers: Doomsday and Avengers: Secret Wars, many are curious about how they will appear in the MCU's Sacred Timeline.
After all, Fantastic Four: First Steps takes place in a separate universe. The film is set in a retro-futuristic 1960s New York, and it seems likely that the Avengers don't exist in this world.
What Could Bring the Fantastic Four to the Sacred Timeline?

The "how" has been established, but the "why" remains on the board. Why do the Fantastic Four abandon their universe and leap to the MCU?
The Big Bad of First Steps is the Devourer of Worlds himself, Galactus (Ralph Ineson), and he's there to do what he does best: Eat planets.
Suppose that Galactus succeeds in satisfying his Earth-sized appetite. Then, the Fantastic Four would no longer have a home. Perhaps this prompts Reed to put his ideas regarding wormholes to use, and the team goes on a voyage through the Multiverse.
If this is the case, the FF's final destination is likely the Sacred Timeline, where the Fantastic Four-Avengers team-up will ensue.
Another potential wrinkle to this explanation centers around Franklin Richards. Reed and Sue's young son Franklin is impossibly powerful due to inheriting his parents' cosmic ray-bathed genetics. It's strongly speculated that Franklin will also have a role in Fantastic Four: First Steps.
Maybe the boy's abilities manifest in First Steps, and he can propel his family to safety from Galactus and into the MCU. Reed's existing knowledge of the Multiverse could assist his son in navigating this journey.