Splicing

Splicing lets a Lightning node resize an existing payment channel, adding or removing funds, without closing it. The change is folded into a single on-chain transaction, and the confirmed splice transaction becomes the channel's new funding transaction. Crucially, the channel keeps operating throughout, so payments continue routing without downtime.

Splice-in and splice-out

A splice-in adds Bitcoin to a channel, increasing its capacity, for example to support larger payments or earn more routing fees. A splice-out removes funds to an on-chain address, letting you spend or cold-store part of a channel's balance without tearing it down. Both fold the resize into one transaction, saving the cost and disruption of a separate close-and-reopen cycle.

Why it matters

Before splicing, changing a channel's size meant closing it (paying an on-chain fee and losing the channel's age and connectivity) then opening a fresh one (paying again and waiting for confirmations). Splicing, standardized in the BOLT specifications as a channel feature, makes capital management on Lightning far more fluid and efficient, especially for active routing operators.

Splicing changes a channel's channel capacity in place and complements liquidity tools like submarine swaps for keeping a routing node well-balanced.