Bitcoin Core 30.0 Changes Default OP_RETURN and Relay Policy
Bitcoin Core 30.0 raised the default data-carrier limit to effectively 100,000 bytes, allowed multiple OP_RETURN outputs, and lowered several relay-fee defaults. The policy changes did not alter Bitcoin consensus, but they became central to the Core–Knots governance dispute that intensified the following month.
Bitcoin Core version 30.0 was released on October 10, 2025, introducing a set of node-policy changes that became some of the year's most contentious technical decisions. Most prominently, the release increased the default `-datacarriersize` setting to 100,000 bytes—effectively removing the previous practical 83-byte OP_RETURN data limit because transaction-size constraints would normally be reached first. It also permitted multiple data-carrier outputs within a transaction and lowered default minimum relay and incremental relay feerates.
These were policy changes, not consensus changes. Bitcoin Core nodes using the new defaults would relay and mine a wider range of otherwise consensus-valid transactions, but blocks did not become valid or invalid under new consensus rules merely because a node upgraded to version 30.0. Operators could also restore the earlier data-carrier limit through configuration. That distinction became essential as the debate around the release grew more heated.
Supporters of the change argued that the old OP_RETURN restriction no longer prevented arbitrary data from being embedded in transactions and that standard relay policy should better reflect transactions miners could already include. Critics, including developers and users aligned with Bitcoin Knots, argued that increasing standardized data carriage encouraged non-monetary uses of block space and could expose node operators to legal or operational risks. Those disagreements were not merely theoretical: they helped drive a visible split in node software preferences and fed a broader argument over what role maintainers, miners, and node operators should play in defining acceptable transaction policy.
Core 30.0 therefore matters less as a routine software release than as the technical trigger for a governance episode. Later October proposals sought consensus-level restrictions on arbitrary data, and in November the dispute escalated into a wider Core-versus-Knots controversy. The release became a reminder that even non-consensus defaults can have political and cultural significance in a decentralized system when they affect what transactions nodes relay and miners are encouraged to include.