NotATether: Create Dual funding stub (BOLT 2 v2 open / option_dual_fund)

2026-09-12T02:51:06Z

Create Dual funding stub (BOLT 2 v2 open / option_dual_fund)

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'''Dual funding''' is a [[Lightning Network]] channel-opening protocol in which both peers can contribute inputs to the funding transaction, so the channel can open with a non-zero balance on both sides. It is the motivating use of the version 2 channel establishment flow in BOLT 2. Feature bits 28/29 advertise <code>option_dual_fund</code>.

The original Lightning open is single-funded: one peer pays the entire funding output and on-chain fees, and the other starts with no outbound liquidity until it receives payments or later adjusts the channel. Dual funding lets each peer put coins into the same 2-of-2 or Taproot funding output in one on-chain transaction.

Peers that support the feature exchange <code>open_channel2</code> and <code>accept_channel2</code>, then build the funding transaction interactively with <code>tx_add_input</code>, <code>tx_add_output</code>, remove messages, and <code>tx_complete</code>, followed by commitment setup and <code>tx_signatures</code>. Because both sides may contribute inputs, the unconfirmed funding transaction can be fee-bumped with [[Replace by fee]] by repeating interactive construction at a higher feerate. Dual funding does not by itself change HTLC routing. Both peers need on-chain UTXOs. A peer with no coins cannot dual-fund.

== See also ==
* [[Lightning Network]]
* [[PSBT]]
* [[Replace by fee]]
* [[Channel factory]]

== External links ==
* [https://bitcoinops.org/en/topics/dual-funding/ Bitcoin Optech: Dual funding]
* [https://github.com/lightning/bolts/blob/master/02-peer-protocol.md BOLT 2: Peer Protocol for Channel Management]
* [https://github.com/lightning/bolts/blob/master/09-features.md BOLT 9: Assigned Feature Flags]

[[Category:Technical]]

Dual funding - Revision history

NotATether: Create Dual funding stub (BOLT 2 v2 open / option_dual_fund)