Bitcoin Core to Remove OP_RETURN Data Limit in October Release, Sparking Debate Over Decentralization and Spam

Bitcoin Core, the reference software for the Bitcoin network, is preparing to lift a nearly decade-old data restriction. Developers have approved a change that removes the long-standing 83-byte default limit on OP_RETURN data, a mechanism used to embed information in Bitcoin transactions.

Set to take effect in version 30 this October, the change replaces the 83-byte cap with a much higher default limit of 100,000 bytes, effectively removing the ceiling on how much data can be embedded via OP_RETURN — up to the broader constraints of transaction and block size limits. Users who prefer the old limit can still set it manually using the "-datacarriersize" option, though that feature is now deprecated.

Why the Change Matters

Originally introduced in 2014 to combat blockchain bloat and spam, the OP_RETURN cap has since been criticized as ineffective. Users can bypass it by sending transactions directly to miners, which some say encourages centralization. Supporters of the new policy argue it brings Bitcoin Core’s default settings in line with actual miner behavior, fostering a more decentralized and permissionless environment for data publishing.

Gloria Zhao, a Bitcoin Core developer and software engineer at Chaincode Labs, said the cap created a "misalignment" in how Bitcoin treats different types of data storage. She explained that the restriction pushed users toward more problematic methods—like using unprunable data structures or making private deals with miners—that strain the network and undermine decentralization.

"By removing this cap, we're encouraging more prunable, transparent use of block space," Zhao said, noting that OP_RETURN data doesn't affect Bitcoin’s UTXO set and is relatively expensive to use, making it a less harmful way to embed data onchain.

Support and Backlash

The move has been praised by many in the community, including well-known figures like Jameson Lopp (Casa), Ben Carman (Spiral), and Alex Thorn (Galaxy). Lopp called it a win for Bitcoin’s open, merit-based development model: “Bitcoin Core just sent a message: Personal attacks and Sybil attacks are ineffective. Meritocracy or bust!”

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But critics remain vocal. Opponents like Jimmy Song and Parker Lewis warn that lifting the cap could invite more spam, clutter the blockchain with non-financial data, and set a troubling precedent for future changes.

Luke Dashjr, Bitcoin Knots maintainer and CTO of Ocean mining pool, denounced the update as enabling abuse of the network. Others, including Jan3 CEO Samson Mow, suggested the change reflects a broader drift toward enabling spam under the guise of openness.

Still, a group of 31 Bitcoin Core developers defended the decision in an open letter, framing it as an affirmation of Bitcoin’s censorship-resistant nature.

“This is not about endorsing non-financial use cases,” they wrote, “but accepting that Bitcoin, by design, can’t and shouldn’t censor transactions simply because they’re unpopular.”

Bitcoin Core development and transaction relay policy

Bitcoin Core development and transaction relay policy

Bitcoin Core.

Not a Consensus Change — Yet Still Controversial

Importantly, this is a mempool policy change, not a consensus rule change. It affects how nodes relay transactions, not what gets mined or accepted by the network. Those who disagree with the decision can use alternate implementations like Bitcoin Knots, which maintain stricter limits.

The original proposal was led by developer Greg Sanders and built with input from Peter Todd and others. Developers considered three options: keeping the cap, increasing it, or removing it altogether. They concluded that the first two were arbitrary and unenforceable, and that a full removal made the most practical and ideological sense.