The Op_return debate has flammed up in the Bitcoin industry in recent weeks and has now invaded most conversational spaces within the industry. This topic is rich and complicated, and many people have strong opinions on this issue.
Op_return is an opcode in the Bitcoin scripting language used to store metadata or any data that is not related to validating a Bitcoin transaction. So it provides developers with a controlled environment pruned by node runners and anchor data on the chain, while allowing for more efficient management of SPAM.
Taking a harm reduction approach to spam issues, the OP_Return controversy was recently sparked by a pull request submitted by Peter Todd to the Bitcoin Core repository. Advocates of the update attempt to rule out any amount of data that can be placed in OP_Return by removing the Mempool policy rule that limits it to 80 bytes. As a result, this moves the limit to a consensus block size cap for 1MB of non-segwit data. They argue that this restriction is no longer effective at stopping spam, and on the contrary, it leads to more harmful behaviours such as UTXOS stuffing that harms node runners.
Furthermore, this proposal removed the DataCarrier flag, a configuration option that allows node runners to choose which transactions to filter from local Mempool based on the amount of data carried by op_return.
Opponents led by Luke Dashjr want to maintain the OP_Return limit and maintain the DataCarrier size, as well as suggesting further Mempool policy restrictions on “non-financial” transactions with any data and Bitcoin.
Both camps generally agree that any data about Bitcoin is bad for the network. They also agree that filters may not be able to filter any kind of spam. What they disagree is how effective these types of filters are in alleviating spam. They also disagree with the impact on node execution costs and the impact on mining centralization as a result of imposing or removing these filters from the network.
Author’s note: Of course, not all supporters of the OP_return change agree with all arguments in favour of the pull request, and not all enemies agree with all arguments against it. This is a general (and perhaps incomplete) overview of various discussions.
Although supported by many core Bitcoin contributors, Peter Todd-led removal of the OP_RETURN limit represents BitCoin’s harm mitigation approach to spam and any data issues.
Todd argues that the current OP_RETURN limit was initially placed to provide spammers with secure and controlled space for any data, and therefore hasn’t served its purpose as businesses and enthusiasts developed minor private mempools such as Mala slipstream.
The op_return limit was introduced after Nakamoto Atoshi left to protect the network from similar spam, but in very different times blocks were rarely full and there were fewer expensive environments. Also, there were few tools to pruning. The software was very inefficient. Many optimizations have been implemented over the past decade, and their cumulative effects have influenced this debate.
Therefore, the Op_return limit was more effective when created first and was more difficult to bypass. Today, NFT and arbitrary data enthusiasts with ambitious projects pressured by the current Mempool limits from the OP_Return space have resorted to packing any data into the UTXO set instead. Unlike Op_return or Segwit spaces that can be reasonably pruned from nodes, UTXO sets are usually kept in RAM, the most expensive memory. The UTXO set must be processed on the node to verify the supply of coins and verify the integrity of the new transaction, which is the fundamental part of running the node. As a result, UTXO data stuffing imposes significant costs on node runners by increasing initial block downloads, overall synchronization times, and ultimately hardware requirements that harm the decentralization of the Bitcoin network.
Finally, supporters argue that miners are “rational economic actors.” This means that in order to stay alive in a highly competitive market, you need to optimize for profit as much as possible. So if mining consensus valid non-standard transactions give them an advantage, they will take it.
In 2023, Luke Dashjr proposed changes that would apply the DataCarrier Mempool policy to Segwit and attempted to apply it to any Taproot data, such as inscriptions, further limiting spammer options. Peter Todd opposed the PR, saying, “The transactions covered by this pull request are a very important source of fee revenue for miners. It is very unlikely that miners will abandon their revenue stream. Censoring these transactions simply encourages harmful things to small miners, but makes rate estimates less reliable.”
Todd’s Pull request did one more thing besides removing the OP_Return limit. I also removed the DataCarrier flag from the node operator configuration options. Users of the Bitcoin Core node software can control transactions relayed through the node based on a configuration option called the DataCarrier flag.
Proponents argue that the flag is now abolished and that the prevalence of tools such as the Mining Pool Mara slipstream program and Todd’s Libre relay is streamlining the inclusion of consensus variant transactions, even if it is “non-standard” by member policy.
Consensus Valid Non-Standard Transactions are inconsistent with Mempool policy rules such as the OP_Return limit, but they do not break the consensus rules, so if the miners are simply able to recognize the transaction, the miners can directly be included in the miners. Such systems, according to already outdated and controversial filters, claims that supporters will make the data carrier’s flag irrelevant, especially if the default op_return size limit is lifted.
Supporters argue that this flag only gives the user an illusion of control, and is a “foot gun” (a tool that is dangerously easy to misuse), and in this case it is not useful to the user.
Finally, removing the data carrier flag along with the op_return limit allows you to remove the bitcoin core conflict and repeated points of controversy. Bitcoin Maximialists who support filters are not the ones who have an opinion on the issue or are able to rally the internet to oppose pull requests.
In 2023, a pull request was made to Bitcoin Core, attempting to change the default Mempool policy for routing bare multisig transactions. This is an old standard used today by NFT protocols such as stamps, ensuring that any data can easily reach the chain and even better not be easily pruned. Pull requests quickly evolved into an Internet flame war between “spamers” and change supporters, suspending integration into Bitcoin Core last week, similar to Todd’s pull request.
By removing the data carrier flags that supporters claim anyway, they argue, this kind of drama can be placed in bed, and Bitcoin’s core contributors can move on to other more pressing issues.
Opposition – Led by longtime Bitcoin Core contributor Luke Dashul, known colloquially as a filter, claims that removing the op_return size limit is a surrender to spammers. Fighting in different ways, if Bitcoin Core continues its current development pass, they simply aren’t going to fold. As a result, interest in Bitcoin Knot has increased. This is an alternative implementation of Bitcoin, particularly maintained by Luke Daschul, allowing Bitcoin users to run their own filters when they fit and fight spam. At the time of writing, Luke’s network analysis shows that over 5% of Bitcoin nodes are running Bitcoin Knots.
Filters and Bitcoin Knot enthusiasts will follow the DataCarrier flag as a rule. They claim that with sufficient numbers, the adjusted node runner has a path that successfully filters out certain spam sets to claim the expansion of what the DataCarrier flag controls, as seen in the 2023 pull request by Luke Daschul. Among them, SEGWIT and TagRoot arbitrary data storage capabilities are also restricted by the DataCarrier flag in node runner control. They are not now.
This point in particular resonates with many people, as seen in the growing number of Bitcoin running implementations of Bitcoin Knots, including changes to this type of Mempool policy, while keeping all other Bitcoin core codes intact.
Several Bitcoin Knot supporters, like Chris Guida, are beginning to talk about user-controlled relay policies or “modular filters” that can be created from refactoring Mempool policy codes and updated by following a specific, actively managed template.
In X, he often argues that “spam filtering is somehow a disadvantageous “cat and mouse game.”
I think that’s ridiculous. The new Fangible Token meta protocol allows you to create filters as quickly as you can create a new TX format before hitting the mainnet. ”
Even the filter recognizes that spam control has limitations, but argues that a hostile environment to spam-related software systems and business models is a good thing, and that even if a more price-independent version goes directly to the miners and pays to block them, it needs to be maintained to stop bad behavior.
This post op_return limit: The battle for Bitcoin over any data was first published in Bitcoin magazine and written by Juan Galt.
