In brief
- Core v30 raises the OP_RETURN limit, letting transactions carry far larger amounts of non-payment data like messages, proofs, or files.
- Critics say the change risks abuse and legal exposure, while supporters argue it provides a cleaner, safer way to handle data.
- Figures including Adam Back and Jameson Lopp have flagged the idea spans ideology, legal questions, and developer politics.
Bitcoin is heading into a pivotal month as its Core v30 update prepares to roll out in October, but its arrival has reopened a long-running dispute over how the network should operate and respond to new pressures.
Core v30 is the upcoming October 2025 release of Bitcoin Core, the network’s reference software client. It introduces a highly contested change: raising the OP_RETURN limit so transactions can carry much larger amounts of non-payment data, such as messages, proofs, or files, that nodes will relay and accept.
OP_RETURN is the feature that makes this possible, allowing extra data to be attached to a transaction without affecting spendable coins.
Supporters of OP_RETURN expansion argue that it provides individuals with a cleaner, safer means of attaching extra data to Bitcoin without clogging up the system, as it remains provably unspendable.
Critics argue that it opens the door to abuse, ranging from spam to illegal content, and risks pushing Bitcoin away from its core purpose as a medium of exchange toward a general data-storage network.
The debate had been around since at least 2010, according to BitcoinTalk forum discussions documented by BitMEX Research.
Some, like Luke Dashjr, have advocated for stricter relay rules, calling non-financial data “spam” and pushing to “filter” and minimize what he sees as misuse of block space. Dashjr is the lead maintainer of Bitcoin Knots, a fork of Bitcoin Core that offers an alternative implementation of the same rules with added features and stricter policy defaults.
Others, including Blockstream CEO Adam Back, warn that introducing moderation or selective filtering sets a dangerous precedent, arguing that it could leave Bitcoin vulnerable to censorship and threaten its survival.
In May, allegations surfaced that the increase in OP_RETURN’s limits is motivated by specific projects that stand to benefit from the changes, with at least one leaked email pointing to Jameson Lopp, chief security officer of Bitcoin custody firm Casa. Lopp denied the allegations that same month. Decrypt has approached Lopp for comment.
Something old, something new
“Since ‘bad transactions’ and ‘bad arbitrary data’ have been hosted by Bitcoin for over a decade now, I see few new questions here, moral or otherwise,” Andrew M. Bailey, professor of philosophy at the National University of Singapore and senior fellow at the Bitcoin Policy Institute, told Decrypt.
Still, the most interesting legal issues the debate has produced are “underdetermined by extant case or statutory law,” Bailey said, pointing to whether legal protections like Section 230 would shield node operators from liability for hosting harmful data.
The changes in Bitcoin Core’s upcoming update also raise questions on whether there is “a difference in legal liability for data stored in signatures or other witness items, addresses, multiple OP_RETURN outputs, or single OP_RETURN outputs,” Bailey said.
Asked about Core v30’s immediate impact, Bailey said the relay policies that performative node-runners implement “will have next to no effect on which transactions are included in blocks, and which arbitrary data is smuggled within them.”
Pseudonymous developer Leonidas, creator of Bitcoin-native meme coin DOG, told Decrypt that the Bitcoin Knots community wants to “censor Ordinals and Runes transactions from the Bitcoin network.”
He accused Dashjr of a “recent reframing of the conversation” around child sexual abuse material on the Bitcoin blockchain in an effort to “manufacture a moral panic and smear anyone who stands in his way.”
Decrypt has approached Dashjr for comment.
“The reality is that this data cannot be removed from Bitcoin, no matter what the anti-Core group says,” Erin Redwing, CEO of Ordinals-based events firm Inscribing Atlantis, told Decrypt.
There is no way “to filter data that already exists on Bitcoin’s blockchain,” Redwing said. “Miners can choose what transactions to include in new blocks they mine, but they cannot remove data that already exists on Bitcoin.”
Still, on a technical level, efforts to “preserve and maintain Bitcoin’s immutable nature are entirely reasonable,” Lorenzo, core contributor to Fractal and founder of UniSat Wallet, told Decrypt.
“We see blockchains as reliable carriers of trust, built on cryptographic algorithms,” he said, adding that, “It is precisely this trust in mathematics—rather than in human discretion—that has allowed such systems to develop long-term value.”
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