Bitcoin Core is the reference implementation of the Bitcoin protocol, serving as a full node that validates and relays transactions while enforcing standard mempool policies like limits on OP_RETURN data size to prevent spam. Libre Relay is a fork of Bitcoin Core developed by Peter Todd that relaxes these policies, allowing larger OP_RETURN outputs, multiple OP_RETURNs per transaction, and full replace-by-fee (RBF) support to enhance censorship resistance. The key difference lies in Libre Relay’s preferential peering with other Libre nodes to propagate potentially censored transactions directly to miners, bypassing Core’s filters.