Okla. Admin. Code § 590:10-1-22
A retired member of the Oklahoma Teachers Retirement System who becomes employed by the State Department of Education for the first time on or after November 1, 2019, shall have the option to remain a member of the Oklahoma Teachers Retirement System subject to any applicable post retirement limitations placed on retired members returning to work, or to participate in the OPERS Defined Benefit Plan or the OPERS Defined Contribution System, whichever is applicable under the laws and rules governing those systems. The election to participate in the Oklahoma Teachers Retirement System or the OPERS-administered systems shall be made in writing within thirty (30) days from the initial date of hire with the State Department of Education and is irrevocable.
Okla. Admin. Code § 590:10-1-22