the rest of the league. they didn't opt out of this because another long term contract is preventing them.
but you may find this interesting:
"The first indication of Oklahoma’s decision on where it’s home will be after 2025, be it in their current home Big 12 Conference or in a new P5 Conference, is where Oklahoma decides to park their 3rd Tier content from July 1st, 2022 to June 30th, 2025”
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https://247sports.com/college/oklahoma/Board/103683/Contents/FOX-SportsBTN-talking-to-OU-about-buying-Tier-3-rights-from-OU-119647264/