Transgender individuals who want to change their gender listed on their US passport no longer must be post-op. However, the application still requires a doctor's note. From CNN:
The doctor's certification must confirm only that the passport applicant has undergone treatment for gender transition. Limited-validity passports for applicants who are in the process of gender transition also will be available under the policy.
Previously, individuals had to provide documentation from a surgeon that sex reassignment surgery had been performed on them, according to the National Center for Transgender Equality.
"Surgery no longer a requirement for changing gender on passport" (Thanks, Rachel Hatch!)