What's the antitrust angle? SAT and ACT are administered by different companies, right? Do Caltech or Harvard have some sort of stake in either of them?
Top schools compete with each for students. Collaborating to keep prices high or keep admissions criteria consistent in a way that reduces competition between the schools would open them up to anti-trust complaints.
But that would be hard to prove. If two gas stations collude to set prices, that violates anti-trust law. But if they just follow suit as they see the other raise or lower prices, that's generally legal, as long as there isn't a secret or understood agreement. I expect the latter is more what's going on here.
But for there to be an antitrust case, consumers or suppliers must have been harmed in some manner to the benefit of the trust. Standardized testing costs are pretty low (especially compared to tuition), and they don't reach the colleges/unis.
Colleges still use race in admissions. They just obfuscate it slightly. For example, they preferentially admit people by zipcode, i.e. by the degree to which the neighborhood is non-white, non-Jewish, and non-Asian. They encourage applicants to write about their experiences with discrimination in their applicant letters. They also accept people scoring in the top percentage of grades at a school (which preferentially admits students from worse schools with lower standards i.e. students from black and Hispanic schools). I assume they use a variety of other techniques as well.
But that would be hard to prove. If two gas stations collude to set prices, that violates anti-trust law. But if they just follow suit as they see the other raise or lower prices, that's generally legal, as long as there isn't a secret or understood agreement. I expect the latter is more what's going on here.