Bitcoin Core OP_RETURN Change Sparks Decentralization Debate

• Bitcoin Core removes 83 byte limit on OP_RETURN
• Developers seek alignment with miners’ practices
• OP_RETURN policy divides community over risks and spam

Bitcoin Core Developers approved a controversial change to the OP_RETURN policy, removing the old default limit of 83 bytes for data inserted into transactions. The change was included in the v30 version of Bitcoin Core, scheduled for release in October, and increases the allowed size to up to 100.000 bytes, now subject only to the default transaction size limit (around 400 KB) and block size limit (4 MB).

While OP_RETURN functionality has historically been limited to prevent bloat and spam, the new policy is intended to reflect practices already adopted by miners, who often accept larger transactions sent directly, outside of the mempool. Proponents of the measure claim that it makes the process more decentralized and less dependent on private agreements with miners.

According to Gloria Zhao , Bitcoin Core developer and Chaincode Labs engineer, the previous limit encouraged less efficient methods and compromised decentralization. “We are fixing a misalignment between cost and standardization of data storage methods,” she explained. She also stressed that OP_RETURN outputs are disposable and do not impact the UTXO set.

However, the adjustment was not unanimous. Critics such as Luke Dashjr, maintainer of Bitcoin Knots and CTO of Ocean Pool, warned of the increase in non-financial data on the network and potential abuse. Parker Lewis, author and Bitcoin educator, called the decision “a horrible precedent” that threatens the decentralized structure of Bitcoin Core.

No, that's nonsense. OP_RETURN is an abuse. Scams are an abuse. Spam should be filtered. Scammers should be jailed.

Bitcoin does not have security budget issues. That's FUD.

— Luke Dashjr (@LukeDashjr) May 17, 2025

The debate over the proposal gained momentum in May, with names such as Peter Todd and Greg Sanders taking part in the discussions. Jameson Lopp of the House praised the decision: “Bitcoin Core just sent a message: personal attacks and Sybil attacks are ineffective. Meritocracy or bust!”

Despite the controversy, this is a change in the mempool relay policy, not a change in the protocol consensus. Users who disagree with the new rule will be able to resort to other implementations, such as Bitcoin Knots, to maintain the previous limit on their instances.