Revert OP_RETURN Policy Changes in Bitcoin Core v0.30 #33619

Proposal to Revert OP_RETURN Mempool Policy Relaxation for Enhanced Network Integrity and User Consensus

I'm a Bitcoin user and node operator requesting a rollback of the OP_RETURN policy changes in Bitcoin Core v0.30. The update increased the data carrier size from 80 bytes to 100,000 bytes, causing concerns about blockchain bloat, spam, legal risks, and Bitcoin's focus as digital cash.

Why Roll Back?

Keeps Bitcoin Decentralized: Large data in transactions bloats the blockchain, making it harder and costlier to run nodes, which hurts decentralization.

Reduces Spam: Bigger OP_RETURN limits could flood the network with non-financial data, raising fees and pushing out regular users.

Avoids Legal Issues: Storing large data on-chain risks illegal content being added, which could cause legal trouble for node operators.

Community Support: Many users on X and Reddit oppose this change. Bitcoin Knots (keeping the 80-byte limit) is gaining node share (~18-20%), showing a community split.

Reverting this will show Bitcoin Core listens to users and keeps Bitcoin focused on being secure money.

How to Roll Back

Here are simple ways to fix this without major changes:

Reset Default Limit: In the next release (v0.30.1 or v0.31), set -datacarriersize back to 80 bytes. Revert changes in src/policy/policy.cpp.

Add a Strict Option: Create a setting like -strict-opreturn (default: on) to enforce the 80-byte limit unless users opt out.

Phase It Out: Gradually lower the limit (e.g., 10,000 bytes in v0.31, then 80 bytes in v0.32) while checking network stats.

Add Anti-Spam Filters: Copy Bitcoin Knots and add optional filters for dust or data-heavy transactions.

These steps keep Bitcoin backward-compatible and respect user choice.

My Take

Please understand: we need to code Bitcoin in a way that keeps it legal and doesn't challenge governments. With huge OP_RETURN limits, there's a real risk of lots of illegal stuff (like CSAM, malware, or copyrighted material) being etched on-chain forever. Node operators could face jail time or fines just for running a full node.

Bitcoin is used by millions as a store of value—not a spam platform or decentralized storage. We do not want unnecessary spam flooding the chain and driving up fees.

We have thousands of altcoins for NFTs, inscriptions, and data storage. Why turn Bitcoin into another one? What's next—switching to PoS? Is that the direction we're taking?

Bitcoin: A Peer to Peer E- Cash System.

Hello @besoeasy I'm going to close this as I don't think that the issue tracker in this repo is the place for this type of discussion at this point: this has already been hashed out in various technical PRs in this repo, as well as on other social forums for multiple years now.

Bitcoin Core v30.0 still includes the -datacarriersize command line flag which you can set to 83 to get ~ the same configuration as a pre-v30.0 node (although it will permit multiple smaller OP_RETURNs up to the total limit, see the release notes for more details).

For proposed protocol changes (an approach better suited to actually prevent certain types of transactions you don't like from being permitted) you can post to the bitcoindev mailing list or the Delving Bitcoin Discorse forum.

Spam attacks are issues