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A Comprehensive OP_RETURN Limits Q&A Resource to Combat Misinformation
29.6k sats \ 12 comments \ @tidwell 11h bitcoin
zaps forwarded to @Murch (51%)
My goal is to share a concise list of questions about OP_RETURN limits that we've answered on Stacker News, as the original thread has become unwieldy with over 200 comments. We began compiling this list about a week ago. I've frequently shared individual links and received very positive feedback. I hope this resource helps us work from a common set of facts and reduces misinformation. I hope you find this as a valuable resource.
I'll list the questions in order of activity and tips received. I've removed duplicates, rephrased some statements as questions, and ignored completely irrelevant questions.
  1. Users should be given clear configurable options to decide what's in their mempool, why were these options taken away? link
  2. Won't spammers abuse large OP_RETURNs to bloat the blockchain and make IBD take longer? link
  3. A similar PR was proposed by Peter Todd 2 years ago, why was it rejected then? What has changed since then, why would this get approved now? link
  4. Shouldn't we be fighting spam, why are we making policies less strict, shouldn't we be making them more strict? link
  5. How would someone get around the standardness policy currently for OP_RETURN size? link
  6. What does "standardness mean" in reference to OP_RETURNs? link
  7. Will more than 1 OP_RETURN per transaction be possible if this PR gets merged? link
  8. What are the current OP_RETURN limits and what restrictions are being lifted? link
  9. Are current relay and mempool policies effective for filtering out spam transactions? link
  10. Is it true that this type of update could affect Bitcoin's decentralization? link
  11. Is it possible to stop the abuse of payment outputs (i.e., bare multisig, fake pubkeys, and fake pubkey hashes) that are used to embed data, thereby creating unprunable UTXOs that bloat the UTXO set? link
  12. What was the main reason /concern to add this PR? ... What will happen if we do nothing? link
  13. If OP_RETURN still cannot stop all the garbage, why is so important to remove it? Does it affect future development / improvements for LN? link
  14. What will be the worst case scenario if users still could set their own limits for OP_RETURN? link
  15. Shouldn't we debate the controversy of this PR on Github since it's where the code gets merged to make these changes? link
  16. What does it mean when someone says "Fix the Filters"? link
  17. Will this open the flood gates and drown out all legitimate onchain activity? link
  18. What can we do to stop spam at the consensus layer of Bitcoin? link
  19. Will Taproot wizards and other spam companies and projects start using OP_RETURN to put jpegs on the blockchain? link
  20. If we prevent these transaction from going into our mempools doesn't that prevent or delay these spam transactions from being mined therefore discouraging the spammers? link
  21. Is it possible to stop abuse of witness data? If so, how? (i.e ordinal theory inscriptions, "jpegs"). link
  22. Is there any conflict of interest with Bitcoin Core and companies like Citrea, in ref to this PR? link
  23. Is there any estimation on how much would this affect fees for the average user, considering external projects (like Citrea) using it? Any possibility that this could saturate the mempool and boost fees beyond reasonable? link
  24. Was this PR initially proposed because of Citrea BitVM needs? If so don't they only need a slight bump in OP_RETURN size, why is it being proposed to make the size unrestricted? link
  25. What makes a UTXO unprunable? Which projects are making unprunable UTXOs? link
  26. Why would a spammer use OP_RETURN if it's cheaper to use Witness data to store arbitrary data? link
  27. Won't large OP_RETURNs allow people to spam the mempool with 100kb transactions and mess up bitcoin for everyone by bloating the mempool and not allowing legitimate transactions in the mempool? link
  28. If relaxing op_return standardness limit seeks to make 'spam' prunable, then what are proponents of this change assuming about the long-term feasibility of running a 'full' (unpruned) bitcoin node? link
  29. Is allowing standardness for larger OP_RETURNs a slippery slope? If we allow this won't we continue to allow things that make bitcoin less for money and more for arbitrary data? link
  30. Won't removing the OP_RETURN cap reduce fee market pressure by allowing senders to consolidate arbitrary data into a single transaction? link
  31. Could this PR be the beginning of reducing other mempool restrictions? link
  32. Culture is what protects Bitcoin from external forces, shouldn't non-technical arguments be valid when considering these types of changes? link
  33. What's the difference between UTXO set, mempool, and blockchain, and how do larger OP_RETURN or witness data affect node resource usage? link
  34. What is the difference in defining a transaction as valid versus defining a transaction as standard and why do we need this difference? link
  35. If you're happy with your viewpoint on consensus and mempool rules, is not upgrading Bitcoin Core until it makes sense to you a valid action to take right now? link
  36. Why didn't this PR get a BIP number? link
  37. Why is core rushing this change? link
  38. If there will be a hard fork resulted from this PR (split chain like in 2017), what will happen with existing LN channels? Will exist on both chains with 2 LNs? link
  39. Isn't this all moot in a (almost guaranteed) future where fees are very high? link
  40. What is this controversy about, and what is it really about? link
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172 sats \ 6 replies \ @LibreHans 9h
For me this isn't about technical details or OP_RETURN any more. Spam is bad. Core making it easier to spam sends the wrong signal. I didn't care about filters before this, now I do.
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210 sats \ 5 replies \ @tidwell OP 9h
@LibreHans If you were to ask "is core allowing more spam by removing OP_RETURN limits?" I think they would not agree they are.
Do me a favor, look at questions 2,4,9,19,20,26,27,28. Is there anything you disagree with in ref to the answers? I would love to make this constructive instead of a "us vs them" sort of thing. Likely we all want something very similar.
question 19 is:
Will Taproot wizards and other spam companies and projects start using OP_RETURN to put jpegs on the blockchain?
Probably closest to really drilling into this and getting the perspective of Udi and Rijndael both active in that question.
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1051 sats \ 10k boost \ 1 reply \ @usagi 5h
Using the word "allow", as in "Is Core allowing more spam by removing OP_RETURN limits", is misleading. Nobody who is making the pro-Knots argument is claiming that mempool policies will affect what is or is not "allowed".
What they are claiming is that OP_RETURN limits disincentivize spammers from creating transactions that violate those limits by making them more expensive. All else being equal, the more expensive it is to spam, the less of it there will be in the blockchain (ironically, this is exactly what many pro-Core people say we need – incentives to guide desirable behavior).
Why do OP_RETURN limits, or in general, any standardness rule, make non-standard transactions more expensive? In several ways (the writeup below is lightly edited from [1]):
  1. If I'm a spammer and I have a transaction that I know won't pass standardness rules, I'll have to go to a miner (or miners) directly via some special side-channel. If you're in control of a major mining pool and somebody comes to you with a transaction that won't pass standardness rules, you've got leverage to charge more (due to strictly lower competition). Not only that, but you know you're damaging your reputation by going against the will of a large part of the community (as expressed via those standardness rules), so you'll want compensation for that as well. The end result is that the transaction becomes more expensive for the spammer.
  2. In the event that two blocks are mined at the same time, one containing nonstandard transactions and the other containing only standard transactions, the block containing nonstandard transactions will propagate through the network more slowly, since nodes will need to download all the nonstandard transactions since they haven't seen them before (or if they have, they would have been filtered out of their mempool). Hence miners are more likely to see the standard block first, and mine on top of that. The nonstandard block is disadvantaged and risks being orphaned. This also makes things more expensive for the spammer since the miner will want to be compensated for this possibility. As a rough estimate, according to chatGPT, this happens about 1-3 times per week.
  3. It will take longer to get a nonstandard transaction into a block compared to a standard transaction. Standard transactions can be mined by all miners, whereas a nonstandard transaction can only be mined by whichever miners have accepted the transaction. Hence on top of the transaction costing more, it will also suffer from greater delay.
  4. Lastly, although a minor point, it's still worth mentioning that going through side channels requires extra effort on the part of the spammer.
These are all very real deterrents to non-standard transactions.
For one data point, see [2] which shows that since the beginning of this year, there have been THIRTY non-standard OP_RETURN transactions out of SEVEN MILLION. This serves both as an example showing non-standard transactions still being "allowed" on the blockchain (what pro-Core people love to repeatedly point out), as well as the effectiveness of the existing OP_RETURN filter. What do you think will happen to the number of non-standard OP_RETURN transactions if we remove this filter?
While I'm at it, I also want to address these arguments about how removing OP_RETURN limits will improve the situation with miner centralization. I think these arguments are incomplete – the real outcome is unclear (although I think more likely a net negative for decentralization).
Divide the miners today into three categories:
  1. Those that don't care about spamming the blockchain, and have access to special deals involving non-standard transactions (call this group "NSA", for non-standard, advantaged)
  2. Those that don't care about spamming the blockchain, and don't have access to special deals involving non-standard transactions (call this group "NSD", for non-standard, disadvantaged)
  3. Those that do care about spamming the blockchain (call this group P, for purists)
Now let's say OP_RETURN limits are removed, what would happen to each of these three groups?
NSA loses its monopoly over non-standard transactions, whereas NSD gains access to lucrative transactions it previously didn't have access to, so NSA loses relative to NSD. This is what the pro-Core people have been arguing. This seems like a good thing. But what about P? Not only do they not benefit from this change, they will likely suffer relative to NSA and NSD. Non-standard transaction spam becomes cheaper (an important point, not to be forgotten, and previously established above) and demand for such spam increases, likely leading to an increase in the overall revenue from spam transactions, which NSA and NSD benefit from but P does not, making P less competitive. And P happens to include entities like Ocean, which play a critical role in the overall decentralization effort.
This is of course all speculative on my part, but my point is merely that this is not a clear win for decentralization, as the pro-Core people have been claiming.
This last argument was edited from [3]. If you had a hard time following, I suggest looking at the parent post for [3], which links to an excellent (pro-Core) overview of the miner centralization issue.
[1] https://xcancel.com/RIPreason/status/1921764767108325772 [2] https://xcancel.com/oomahq/status/1916793928025596338 [3] https://xcancel.com/RIPreason/status/1921693384785420505
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0 sats \ 0 replies \ @usagi 1h
More stats on the OP_RETURN filter, confirming that yes, it makes spam more expensive:
https://xcancel.com/jimmysong/status/1922112890980729156
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50 sats \ 2 replies \ @LibreHans 8h
Like I said, this isn't about technical details any more. My views on bitcoin, individuals in the project, and their motivations, have changed.
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33 sats \ 1 reply \ @SimpleStacker 5h
What would you propose as a better course of action?
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0 sats \ 0 replies \ @LibreHans 1h
For starters, core devs could not have tried to take away configuration options, and could not have attacked people who were unhappy about that. I'd like to see a well maintained alternative to "core".
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10 sats \ 3 replies \ @Jerrian_thedeep 8h outlawed
stackers have outlawed this. turn on wild west mode in your /settings to see outlawed content.
0 sats \ 0 replies \ @Jerrian_thedeep 9h outlawed
stackers have outlawed this. turn on wild west mode in your /settings to see outlawed content.