The Bitcoin community is witnessing an unprecedented escalation in the so-called 'OP_RETURN War of 2025' after a single transaction filled an entire block with nearly 1 megabyte of arbitrary data. Block 896,696, mined on May 15, 2025, by Marathon Digital Holdings (MARA), contains a non-standard OP_RETURN output that drastically exceeds the conventional 80-byte limit, marking the largest OP_RETURN in Bitcoin history.
The Battle Over OP_RETURN Limits
OP_RETURN is a Bitcoin script opcode that allows embedding up to 80 bytes of unspendable data without bloating the UTXO set. It is commonly used for timestamping, asset issuance, and inscriptions. However, the 80-byte cap has long been a point of contention. A recent Bitcoin Core proposal to remove this restriction has sparked fierce debate among developers and on social media. Critics warn that lifting the cap could lead to chain spam, while proponents argue it would eliminate the need for complicated workarounds.
Amid the policy discussions, creative users have turned OP_RETURN into an unconventional medium for expression. One memorable message cleverly riffs on Rick Astley's 1987 hit: 'Never gonna give you OP_RETURN. never gonna let you down Never gonna run around and desert you Never gonna make you cry, never gonna say goodbye Never gonna tell a lie and hurt you.' Another reads: 'Filters have a huge influence on what gets mined.'
Block 896,696: The First '1 Megger'
The record-breaking block was crafted by a group known as The Wizards of Ord, who inscribed their entire collection of 3,333 Ordinal inscriptions within a single OP_RETURN transaction. 'We just created the largest OP_RETURN in Bitcoin history,' tweeted account @lifofifo. 'Introducing the first-ever 1 megger, Block 896696, which includes every single The Wizards of Ord in OP_RETURN data.'
Building a transaction that could occupy an entire block required the creator to circumvent multiple policy-level constraints. Since the 80-byte cap is enforced only by default standardness policies (not consensus rules), the transaction was flagged as non-standard and submitted directly to Marathon's mining pool, which opted to ignore default policies and include it. The transaction used Bitcoin v2 (SegWit) format, sent 0 BTC, and carried a generous fee that incentivized miners to include it despite its inefficiency in fee-per-byte ratio.
Node Operators Respond with Filters
The surge in OP_RETURN experimentation has coincided with a notable increase in adoption of the Bitcoin Knots node implementation. Unlike the upcoming Bitcoin Core release, Knots retains the -datacarrier and -datacarriersize flags, giving operators granular control. Setting -datacarrier=0 allows a node to reject all OP_RETURN transactions, while modifying -datacarriersize enforces stricter data caps such as the conventional 80-byte limit. These parameters filter incoming transactions from a node's mempool, stopping their propagation to peers.
Knots now runs on roughly 2,000 nodes, up from just 600 in mid-March, though this still trails the 19,470 publicly visible Bitcoin Core nodes currently online. The divergence illustrates a growing tension between those who want to preserve Bitcoin's original P2P payment vision and those who see it as a platform for data embedding and creativity.
As the network navigates this quiet redefinition—where policy, purpose, and participation are tested one byte, one block, and one meme at a time—the outcome of the OP_RETURN War will likely shape Bitcoin's future as either a peer-to-peer cash system or a store of memes and data.