BTC's 81000 Call OI Spike Traces to Real Block Buying, Not Dealer Noise

BTC's 81000 call (18SEP26 expiry) open interest rose from 194.5 to 332.9 contracts in 24 hours — a 71.2% build adding roughly $11.2M notional, one of the sharpest single-strike moves on the board. Pulling the taker tape apart by the hour shows this wasn't quiet dealer-internal hedging: it was concentrated, aggressive buying.

Window	Net volume	Buyer aggression	Block trades	Block net USD
24h aggregate	+235.5	0.80	10	$16.13M
15:00-16:00 UTC	+220.0	0.895	9	$18.16M
16:00-17:00 UTC	-25.0	0.00	1	-$2.03M

Net premium over 24h landed at +$502,936, buyer-dominant. Zooming out to the whole expiry, the same skew holds: call OI added 893.2 contracts versus 119.3 for puts, with the desk's own dominant-side read tagged call_buying. Neighboring strikes echo it — 82000C buyer aggression 0.91, 83000C 0.85.

Taken together, this looks like fresh directional call exposure entering through block channels rather than a delta-neutral market-maker rebalance. The one $2.03M block sold back an hour later suggests part of the position was trimmed almost immediately, but it didn't reverse the net buy-side tilt.