But the deal comes with a release clause that keeps a door open for a small number of elite clubs.
The 26-year-old centre-back had been the subject of interest from Real Madrid, Liverpool and Manchester United, and his previous deal was due to expire at the end of next season. Months of negotiation have finally produced an outcome, with the German international choosing to stay rather than leave in the summer.
According to Kicker, Schlotterbeck will earn a base salary of €10 million per year with bonuses of up to €4 million. The contract also includes a release clause in the €50-60 million range — described by Bild as a "World Cup clause" applicable only to a select few dream clubs, with Real Madrid and Bayern Munich among them.
Crucially, the clause is understood to be valid from this summer, meaning a move could still come this year if one of those elite clubs moves.
CEO Carsten Cramer was clear about what the extension means to the club.
"The contract extension with Nico Schlotterbeck is of enormous importance. He is of great value to us, both as a player and as a person. And Nico in turn knows exactly what he has in our club."
Cramer outlined the mood around the project at Signal Iduna Park.
"He is highly valued and feels that we are building something here. Therefore, we are very happy that we were able to extend his contract, which was due to expire next year, at an early stage."
Schlotterbeck himself said the process was worth taking slowly.
"I am incredibly happy to have extended my contract with BVB. I deliberately took my time with the decision because it is important to me. We had good discussions all the time, but it was not a process that was completed in just a week or two."
He explained what convinced him to commit.
"The club's management presented me with a good plan, and I know what I have to offer at this club. My goal is to win titles with Borussia Dortmund."
Schlotterbeck joined from Freiburg in 2022 and has made 155 competitive appearances for the club, contributing 10 goals and 18 assists. He has 25 caps for Germany and is expected to be a key figure at this summer's World Cup.
The extension secures Dortmund's defensive cornerstone on paper — but that release clause ensures the transfer conversation around Schlotterbeck is far from over.