A 97-kilobyte PNG appeared in a single OP_RETURN in May 2025. Relay policy capped OP_RETURN at 80 bytes. How did it get mined?
MARA mined block 896,088 with a 97,446-byte picture stuffed into one OP_RETURN — months before Bitcoin Core v30 lifted the relay cap.
The appearance
For eleven years the social contract around OP_RETURN was: 80 bytes, one output, pay the fee, do not bloat the UTXO set. Then a full PNG, 97,446 bytes, landed in a single OP_RETURN. Ordinary nodes would not relay that transaction. It is in the chain anyway.
Case file sealed
Investigation notes, the reconstruction, and sources sit behind this seal. Open it when you have sat with the raw transaction.
Open the case file
The investigation
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01 Relay is not consensus
Bitcoin Core’s default mempool policy is a courtesy, not a law. Consensus has allowed much larger scripts for years (up to 10,000 bytes in a script, and larger transactions). If you do not need the public mempool — if you hand the hex to a miner — policy never sees it.
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02 MARA’s side door
MARA Pool had been mining out-of-band transactions (Slipstream and similar) for customers who wanted inscriptions or large data without waiting for Core policy. Bitquery flags this PNG as mined by MARA before Core v30 raised the default OP_RETURN relay limit to ~100 KB in October 2025. The picture is a proof of the side door.
Reconstruction
Not a consensus exploit. A miner accepted a transaction the public gossip network would have dropped. The OP_RETURN cap everyone quoted was a relay default. MARA, paid to include the bytes, wrote them into block 896,088. Core v30 later made the same size relayable for everyone, which is why 2026’s chain looks like a billboard.