The midfielder has signed a first pro deal with Arsenal after spending the past two seasons with Derby.
“I'm just very pleased, obviously playing for a big club. Can't wait to get started and play for Arsenal," Agustien told arsenal.com.
“I think the way they’ve got the ex-pro footballers here as well, which is something big within the club.
“Obviously, you've got the likes of Per (Mertesacker), which I've obviously spoken to as well, and I know his values.
“They're very high and he wants to create a better player, but also a better person, which is a great statement as well.”
Agustien is the son of former Swansea City and Crystal Palace midfielder Kemy Agustien.
He added, “My dad has played professional football as well before. He played for the likes of Swansea, Brighton, Crystal Palace, really good to be fair.
“He helps me a lot as well and so does my mum as well. So good combination to have."