Okla. Stat. tit. 74, § 916.2

All claims for payment of the death benefit, unpaid accumulated contributions of a deceased member or the final monthly benefit must be made within three (3) years of the date of death of the member. If no claim is made within three (3) years, payment of these monies shall no longer be due and all such monies shall be forfeited to the System in the Oklahoma Public Employees Retirement Fund.