Rice “recommends” but does not require Subject Tests.
https://futureowls.rice.edu/futureowls/Standardized_Tests.asp
The question of whether Subject Tests are truly optional for these colleges has been asked in other threads, including:
http://talk.qa.collegeconfidential.com/college-admissions/2027962-sat-subject-tests-are-not-truly-optional-for-middle-upper-middle-class-applicants-at-elite-colleges-p1.html