Full RBF

Full RBF means a node accepts any fee-bump replacement of an unconfirmed transaction - regardless of whether the original signaled BIP-125 opt-in RBF. In other words, all unconfirmed transactions are treated as replaceable.

Bitcoin Core added full RBF as an option in v24 (late 2022), made it the default in v28.0 (October 2024) and removed the option in v29.0 (April 2025). Every Bitcoin Core node from 29.0 on runs full RBF, so the practical guarantee that "an unsignaled transaction won't be replaced" no longer holds.

The argument for full RBF:

• It simplifies fee policy. Wallet implementations no longer need to track or care about the RBF-signaling bit.
• It reflects the underlying reality. Miners always could mine whichever conflicting transaction paid them more; opt-in RBF was a relay-layer politeness, not a consensus rule.
• It improves user experience for senders who need to bump fees.

The argument against:

• It further erodes zero-confirmation payments. Merchants relying on "I saw it in the mempool" for instant settlement have to either wait for one confirmation or accept the risk of a replacement attempt.
• It shifts the burden of "is this safe to act on?" onto merchants and exchanges, who must wait for confirmations.

Zero-conf was always weakly secure, and full RBF made the weakness obvious. The practical answer for instant payments is Lightning, which is genuinely instant and final. For on-chain, wait one confirmation. Trusting an unconfirmed transaction because most people don't bother to replace one stopped making sense once Bitcoin Core nodes began relaying replacements by default.

See Replace-by-Fee (RBF) for the opt-in flavor full RBF extends.