OP_RETURN: One of the most serious BTC controversies

Written by: Liu Jiao Lian

Recently, a proposal to remove the size limit on additional data carried by OP_RETURN in the Bitcoin Core client has caused a stir in the industry. Typical proponents, such as developer Peter Todd, have repeatedly submitted PRs (Pull Requests), demonstrating a determination to not rest until their goal is achieved.

On July 23, 2023, Peter Todd submitted PR#28130, proposing to remove the restriction on data carried by OP_RETURN. The PR was closed and not accepted.

On April 28, 2025, he remained undeterred and submitted the same proposal PR#32359 again. He aggressively demanded not only the removal of the additional data restrictions but also the deletion of configuration options to prevent client software users from enabling restrictions themselves.

The proposal was opposed by the majority.

Another developer, instagibbs, proposed a slightly more moderate suggestion PR#32406. He suggested temporarily keeping the configuration options but not imposing restrictions by default.

This proposal also has more support than criticism. Instagibbs also wrote an explanation for this, detailing the origin of OP_RETURN and why such a change is being proposed.

Typical opponents include developer Luke Dashjr. He is the maintainer of the Bitcoin Knots client software and was a fierce opponent of inscriptions two years ago. Specific details can be reviewed in previous articles by the teaching chain.

For the average reader, to simply understand this issue, we can use the following metaphor:

Remove additional data restrictions + Virtual machine execution of additional data = Ethereum

Of course, it's not that simple in reality. The Bitcoin ledger uses a stateless UTXO model, and modifying the ledger to store state data (which leads to new problems, namely state explosion) would bring it closer to Ethereum's design.

In any case, it was because Bitcoin Core rejected Vitalik Buterin's proposal to use the additional data capability of the Bitcoin ledger to realize his vision of smart contracts that forced him to establish the Ethereum project.

In this cycle so far, those who bet on Ethereum outperforming BTC must have a lot of prairie animals racing through their minds.

Since this capability is just a feature of the client software and not part of the Bitcoin protocol consensus, there is no need to worry that this dispute will lead to a hard fork like that of 2017.

The main reasons for support include: many modified clients have long canceled this restriction and have received support from certain mining pools; it may bring more incentives to miners; the restriction of OP_RETURN cannot prevent people from cleverly using other capabilities such as multisig and taproot script to carry data, and instead, the restriction leads to the fragmentation of UTXO by forcing the splitting and stitching of data; it is better to allow than to block, and there is no one-size-fits-all method to accurately identify what constitutes garbage data, which is destined to be a futile cat-and-mouse game; and so on.

The main reasons for opposition include: lifting data restrictions may cause the Bitcoin ledger to expand rapidly, thereby weakening decentralization; it could lead to a large number of non-financial applications, diluting the positioning of BTC and reducing it to a mere checkbook; and so on.

According to statistics from Clark Moddy Bitcoin, the current size of the Bitcoin blockchain is approximately 748.1GB, with OP_RETURN additional data accounting for about 3.83GB, or approximately 0.5%.

There is currently no definitive conclusion that the relevant PR will be merged and released. However, based on the results of the community vote, the number of nodes using the slimmed-down version of Bitcoin Knots has already surpassed the number of nodes running the latest version of Bitcoin Core 29.0.

Perhaps we will witness a historic moment: Bitcoin, as a consensus, does not necessarily have to rely on a single dominant client software. (Although this is a fact, many people are simply not aware of it.)

A diversified Bitcoin ecosystem, with two to three equally matched Bitcoin client software, codebases, and development teams competing with each other, following a set of Bitcoin consensus, being harmonious yet different, and contending without breaking, could it instead highlight the charm of Bitcoin's decentralization?