Splicing
Also: splice in, splice out
lightning · advanced
Adjusting the capacity of an open Lightning channel by adding or removing on-chain funds, without closing and reopening it.
Pre-splicing, the only way to grow a channel was: close it on-chain, wait for confirmation, open a new bigger channel. That costs two on-chain transactions, the routing-history of the original channel, and any in-flight HTLCs.
Splicing replaces all that with a single funding-transaction swap. The channel's funding output is spent into a new, larger (or smaller) funding output in a single on-chain transaction. The channel ID changes but the channel keeps operating throughout — payments queue and resume seamlessly.
Splicing was deployed by Phoenix wallet and Core Lightning starting in 2023 and is the basis for sleek user flows like "your wallet automatically opens channels and grows them as you receive more bitcoin." It's a quiet but significant UX unlock for self-custodial Lightning.