Opinion of the Court
private dispute resolution: lower costs, greater efficiency and speed, and the ability to choose expert adjudicators to resolve specialized disputes.” Id., at 685. Class arbitration lacks those benefits. It “sacrifices the principal advantage of arbitration—its informality—and makes the process slower, more costly, and more likely to generate procedural morass than final judgment.” Concepcion, 563 U. S., at 348. Indeed, we recognized just last term that with class arbitration “the virtues Congress originally saw in arbitration, its speed and simplicity and inexpensiveness, would be shorn away and arbitration would wind up looking like the litigation it was meant to displace.” Epic Systems, 584 U. S., at ___ (slip op., at 8). Class arbitration not only “introduce[s] new risks and costs for both sides,” ibid., it also raises serious due process concerns by adjudicating the rights of absent members of the plaintiff class—again, with only limited judicial review. See Concepcion, 563 U. S., 349; see also Stolt-Nielsen, 559 U. S., at 686 (citing Ortiz v. Fibreboard Corp., 527 U. S. 815, 846 (1999)).
Because of these “crucial differences” between individual and class arbitration, Stolt-Nielsen explained that there is “reason to doubt the parties’ mutual consent to resolve disputes through classwide arbitration.” 559 U. S., at 687, 685–686. And for that reason, we held that courts may not infer consent to participate in class arbitration absent an affirmative “contractual basis for concluding that the party agreed to do so.” Id., at 684. Silence is not enough; the “FAA requires more.” Id., at 687.
Our reasoning in Stolt-Nielsen controls the question we face today. Like silence, ambiguity does not provide a sufficient basis to conclude that parties to an arbitration agreement agreed to “sacrifice[] the principal advantage of arbitration.” Concepcion, 563 U. S., at 348. This conclusion aligns with our refusal to infer consent when it comes to other fundamental arbitration questions.
