Members who have accumulated five (5) or more years of creditable service in the public schools of Oklahoma, on which retirement contributions have been remitted, and whose account had not closed prior to July 1, 2003, in accordance with 70 O.S. § 17-103(6) or OAC 715:10-7-3, shall be granted an indefinite extension of membership in TRS. Such membership is vested and shall remain open until the member retires or the contributions are voluntarily withdrawn. Military and out-of-state service shall not be included in the five (5) years required for vesting. Any year of service obtained by the use of accumulated unused sick leave cannot be included in the five (5) years required for vesting. Any member who joins TRS after July 1, 1991, shall be required to have five (5) full years of service credit awarded pursuant to OAC 715:10-3-1 et seq. as a contributing member of the System. Any member who joins TRS after November 1, 2017, shall be required to have seven (7) full years of service credit awarded pursuant to OAC 715:10-3-1 et seq. as a contributing member of the System. For members who join after July 1, 1991, Oklahoma service purchased after membership will not be counted for "vesting" purposes.
Okla. Admin. Code § 715:10-7-1