OP_RETURN data limit faces debate over removal of 80-byte cap

OP_RETURN is a Bitcoin (CRYPTO:BTC) script opcode introduced in Bitcoin Core 0.9.0 that allows users to embed up to 80 bytes of arbitrary, unspendable data within transactions.

This feature enables applications such as timestamping, metadata embedding for layer-two protocols, and coin burning without bloating the unspent transaction output (UTXO) set.

The 80-byte limit, set in 2014, was designed to prevent excessive data storage on the blockchain while permitting essential nonpayment uses.

Projects like Counterparty and Citrea have utilised OP_RETURN to embed digital asset information and zero-knowledge proofs respectively.

However, a debate has emerged over whether the 80-byte cap remains appropriate as some miners and services already accept larger, nonstandard data transactions that increase UTXO size.

Bitcoin Core developers plan to remove the default 80-byte limit and allow multiple OP_RETURN entries per transaction in an upcoming release, though no changes have been merged as of May 12, 2025.

Advocates argue lifting the cap would simplify transaction construction, improve fee estimation, and reduce harmful workarounds like fake multisig scripts that inflate the UTXO set.

“Any operation achievable with OP_RETURN can be replicated through fake addresses at a higher cost to the network,” one developer explained.

Critics warn that larger data embeds may encourage blockchain bloat, increase costs for users, and concentrate power among mining pools prioritising data-heavy transactions.

Some node operators prefer clients like Bitcoin Knots, which enforce stricter anti-spam policies and limit nonpayment data to prevent unnecessary blockchain growth.

Importantly, the proposed change affects only Bitcoin Core’s relay policy and does not alter consensus rules; nodes can still enforce their own OP_RETURN limits.