Splicing

Splicing is a Lightning Network technique that lets participants add funds to or remove funds from an existing payment channel without closing it. Instead of shutting the channel and opening a new one, which requires two on-chain transactions, the parties cooperatively sign a single replacement funding transaction. The channel keeps routing payments while the splice confirms on-chain.

Why it matters

Lightning channels lock a fixed amount of bitcoin when they open, and before splicing the only way to resize one was to tear it down. That wasted fees, destroyed accumulated routing history, and left the channel offline while transactions confirmed. Splicing makes channel capacity fluid: a node can top up liquidity, pay an on-chain invoice directly from channel funds, or withdraw profits, all without interrupting service. Implementations such as Core Lightning and Eclair shipped support around 2023, and mobile wallets built on splicing can hide the channel concept from users entirely.

How it works

Both channel partners negotiate a new funding transaction that spends the current 2-of-2 multisig output, adds or removes the desired funds, and creates a new multisig output for the resized channel. Commitment transactions are maintained for both the old and new funding outputs until the splice confirms, so neither party is ever exposed. Once the replacement transaction is buried under enough blocks, the channel continues under its new capacity as if nothing happened.