Multipath Payments (MPP)

Multipath Payments (MPP), specified in BOLT 4, let a Lightning node split a single payment into several smaller shards and route each one over a different path before they are recombined by the recipient. The technique exists because no single channel may hold enough outbound liquidity to carry a large payment on its own, while the network as a whole usually does. By using many thin paths instead of one fat path, MPP raises the effective payment size a node can send and makes routing far more reliable.

Why splitting helps

Each shard travels as its own onion-routed hop sequence, and every shard shares the same payment hash as the others. The receiver waits until shards summing to the full invoice amount arrive, then releases the preimage to claim all of them. Because the shards reuse one hash, observers can in principle correlate them, and a receiver could reveal the preimage before the full sum lands. This is the key distinction from Atomic Multipath Payments, which give each shard a unique hash and a cryptographic all-or-nothing guarantee.

Practical impact for node runners

MPP improves the success rate of larger transfers and helps drain or balance liquidity across several channels in one payment. Most wallets and routing nodes enable it by default, splitting opportunistically when a single-path attempt fails. Sovereign Bitcoiners running their own node benefit because MPP reduces dependence on any one well-funded channel and lets a modest set of channels carry meaningful payment volume.

MPP builds directly on the conditional-payment primitive described in our HTLC entry, and the shards traverse the network using the same mechanics covered under routing.