The 18-year-old centre-back joins from Tottenham 29 years after his dad, Matthew Upson, did the same at the same age back in 1997. Having grown up around the game through his father's career, Elijah says the decision to commit his future to Arsenal came down to the environment he found at the club rather than the family connection alone.
"When I met the guys here recently and met all the team and staff, it just seemed like a really nice environment," Upson said. "That was probably the biggest factor, an environment where you feel you can hopefully learn and get better as a person."
He added: "It's a great feeling, really proud to be here. [It's] really nice to have all my family and everyone around it, it's been a great experience.
"My dad signed here around the same time as me, it's great to have someone with a good experience of the place. But at the same time, I'm definitely looking forward to building my own reputation and getting started."
A commanding presence at the back, Upson also sees goal threat as part of his game, alongside a passing range he is keen to keep developing.
"Aerially, I'm quite good, it's definitely a strength of mine. Obviously, I'm a defender, but if I can take that into an attacking side of things, then that's also really good and an area I can use that quality as well.
"I'd also say I've definitely worked hard in terms of my passing range and having a good, longer passing range. I'd say that could be a good strength of mine; I'm looking forward to making those qualities better."
Arsenal's first-team centre-back pairing was a particular draw for the teenager as he weighed up his future, with William Saliba and Gabriel Magalhaes held up as the standard to aim for.
"I think definitely the centre-back partnership in the first team that there is between Saliba and Gabriel, they're a good inspiration and really experienced, high quality players. They've had a great season, definitely two players that I'm really keen to learn from and expose myself to hopefully."
Upson will now return to first-team training with Arsenal's Under-21s as preparations continue for the new season, with the defender hopeful of picking up minutes across multiple age-group competitions before pushing for further first-team exposure.
"[I'm hoping for] some exposure to the first team, obviously building a good foundation of games in the 21s and different competitions in the 21s. Hopefully great exposure to the players that are here, and improving."
The deal remains subject to the completion of standard regulatory processes.