The OP_RETURN discussion is not new and dates back to 2014 when Bitcoin Core 0.9.0 was released with the OP_RETURN policy included which was intended to discourage more egregious forms of spam. At that time, 40 bytes was the default max datacarriersize limit across all node implementations; this was and still is sufficiently large for tying data to a transaction (32 bytes for a hash and 8 bytes for a unique identifier). Core subsequently increasing the default to 80 bytes was an entirely voluntary decision and in no way contradicts the design objective that OP_RETURN creates a provably-prunable output to minimise damage caused by data storage schemes, which have always been discouraged as abusive. There are also other good technical reasons which I have chosen to retain the lower default in Bitcoin Knots, and no justification for increasing it.

It is not my intention, nor that of my team at
@OCEAN, to filter coinjoins. These present an innovative tool for increasing Bitcoin’s privacy and, when constructed properly, coinjoins can easily stay within the OP_RETURN limit (indeed, there is no reason for them to have *any* OP_RETURN data at all). I have some ideas on how to alleviate the recent issue where some coinjoin transactions were flagged as spam from Knots v25, and I am willing, with the full resources of my team, to work collaboratively on a solution in good faith.

Bitcoin does and always has allowed nodes to set filters based on multiple sets of criteria and Knots v25’s defaults are IMO what is best for Bitcoin at this time. Others may disagree and that is ok. They are free to (and should) run their own nodes - it is good for Bitcoin to have more people running nodes, including miners, and there should be a natural diversity in node policies. As was stated before, OCEAN is on a path to decentralization and very soon we are going to be in a position where hashers will be able to fully participate as miners and perform the intelligent parts of mining such as deciding which version of node software to run and what filters or other policies to apply to block template construction.