Subject: Re: [bitcoindev] Does anyone still need testnet3?

From: Sjors Provoost <[email-masked]>
Date: Tue, 1 Apr 2025 11:06:05 +0200

Hi Sanket,

I've heard before from some lightning folks that migrating to testnet4 presents a chicken-egg problem.

If we were to start rotating test networks a frequency of e.g. once every three years, this would become a recurring problem.

Lightning seems to be a special case because it relies heavily on interoperability, and so any move has to be coordinated between multiple parties each with their own priorities.

At the same time Lightning software often needs the latest and greatest Bitcoin Core version e.g. for its new policy features. So sticking to v29 back-ports isn't a long term viable option.

I think it's worth considering for the lightning industry to organize a custom signet, either a 1-of-N with keys distributed among the current players, or unsigned proof-of-work based (more hassle, but future new players may feel more comfortable joining). Such a network can be kept online definitely and its replacement can be more easily coordinated. Another advantage is that soft fork proposals can be tested, similar to how Inquisition does that on the default signet, but at a pace that matches Bolt spec work.

- Sjors

> Op 31 mrt 2025, om 23:15 heeft Sanket Kanjalkar <[email-masked]> het volgende geschreven:
> 
> Hi Sjors, 
> Thanks for asking. Block/Cashapp relies on testnet3 and can't migrate to testnet4 mostly because of lack of lightning LND peers.
> I don't think there are any LND Lightning peers on testnet4. We (Block/Cashapp lightning) use LDK for Lightning, but most of our peers run LND. LND support for testnet4 was just merged <https://github.com/lightningnetwork/lnd/pull/9620>, so it’ll likely take time for the LND community to update node infrastructure.
> We want to catch peering, business logic and lightning implementations interoperability issues in testnet. Even though LDK supports testnet4, switching now isn’t viable for us until our mainnet LND peers migrate. 
> 

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