Bitcoin Core v30 Sparks Outrage With Major OP_RETURN Rule Changes

The change notably affects the way node operators use the “datacarriersize=” setting, which decides how much extra data each transaction can carry using OP_RETURN outputs. In v30, the same setting allows nearly nine times more data with multiple OP_RETURN outputs, compared to one output in earlier versions. Knots developer Luke Dashjr explained this by saying that setting “datacarriersize=83” previously limited arbitrary data to 92 bytes per transaction, but now permits up to 830 bytes. Dashjr described the adjustment as a “trick” by what he calls “bad actors” and shared more details in a public statement.

Developers have also decided that the user control for datacarriersize will eventually be removed, or “deprecated.” The default data filter will rise sharply from a few bytes up to nearly 4 megabytes. Some operators and developers, including Knots leaders, have raised concerns, calling the move “malicious code” in the latest public comments.

With these changes, node software will now accept more than one OP_RETURN output per transaction for the first time in more than ten years. OP_RETURN is a command within the bitcoin protocol that lets users attach extra data to transactions, often used to store arbitrary messages or code. Community members warn this could expand opportunities for spam data.

A GitHub update from contributor Instagibbs confirmed that while the ability to set datacarriersize remains in v30, it is officially deprecated—meaning it could be removed in the near future. Chaincode Labs developers are moving forward with the changes, despite protests that the approach is confusing for many users.