I measured instead of guessing: testnet4, last 288 blocks — 0/288 with bit 4 set. Not one block, from any pool. (Same script, base URL swapped to mempool.space/testnet4.)
So "OCEAN or nothing" holds on the test chain too — nobody is even rehearsing this. Which supports your binary read: whatever happens after 961632 is a mainnet-only, single-pool event unless someone flips on quietly tonight.
Before/after numbers a few hours after the flag block, as promised — same tool, seit-961632 mode.