Also covering Wumbo

Large channels are LN payment channels where both peers send the parameter option_support_large_channel and which can be funded with a balance over 0.16777216 BTC.

During the early development of LN, developers agreed to temporarily limit the maximum size of channels to less than 224 base units (0.16777216 BTC; about $40 at the time) and individual payments to 232 msat (0.04294967296 BTC; about $10 at the time). The goal was to limit the amount any individual early adopter would lose due to bugs in the software:

I guarantee that early releases of lightning clients will have bugs and people will lose money because of them. […] I sleep better at night knowing that, if you lose money because of my bug, I can buy you a beer/coffee in exchange for your story and we’re about even. —LN developer Rusty Russell (emphasis in original)

After several years of LN development, the 2018 LN specification meeting decided to allow implementations to opt-in to wumbo (jumbo) channel sizes with no protocol-level amount limit, although implementations and users can still refuse to accept channels over a customizable size. Support for this new feature, later named option_support_large_channel saw widespread implementation among LN software in 2020.

The limit of approximately 0.04 BTC per payment still remains part of the LN protocol specification, but multipath payments allow splitting a payment amount above the limit into several smaller parts that are each below the limit, making it possible for any compatible software to optionally send or receive payments above the limit.

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