This is where Ark's greatest achievement comes in. Many people can take part in an Ark refresh at the same time, and yet the transaction size does not grow in proportion to the number of participants; it stays fixed. In other words, unlike other onchain transactions, the transactions generated by Ark activity don't consume block space exclusively for a single person. They consume truly O(1) block space, which is qualitatively different from something like the batched withdrawals commonly seen at exchanges (a batched withdrawal needs as many outputs as there are recipients).
So, taking all of this into account, Ark scales Bitcoin significantly, but in a completely different direction from Lightning. To use internet speed as an analogy, Lightning offers low latency, while Ark offers high throughput. Ark doesn't guarantee Lightning-level immediacy for large amounts, but in most transactions, amounts above a certain size don't really need immediacy anyway; what matters is throughput. And once full ownership has been secured through a refresh, I can spend freely from then on. The resulting VTXOs will still be marked as theoretically double-spendable, but since the only person who could double-spend them is me, their safety is guaranteed.
Ark also lets users send and receive payments and transfers across ASPs "atomically" through the Lightning nodes run by ASPs, without bearing the burden of running a node themselves. This should vastly improve on Lightning's weakness in reliability and dramatically reduce failure rates. Being able to receive without keeping anything running is another great advantage.
Of course, users do bear a liveness requirement. It's true that anyone who wants a fully unilateral exit needs to be fairly diligent about maintaining that liveness. But only those who want that need to do so.
In conclusion, I believe Ark can be called self-custodial when used with a precise understanding of how it works, and I expect that, thanks to its overwhelming convenience, it will play the most important role if a world where people pay with bitcoin ever arrives.
So, taking all of this into account, Ark scales Bitcoin significantly, but in a completely different direction from Lightning. To use internet speed as an analogy, Lightning offers low latency, while Ark offers high throughput. Ark doesn't guarantee Lightning-level immediacy for large amounts, but in most transactions, amounts above a certain size don't really need immediacy anyway; what matters is throughput. And once full ownership has been secured through a refresh, I can spend freely from then on. The resulting VTXOs will still be marked as theoretically double-spendable, but since the only person who could double-spend them is me, their safety is guaranteed.
Ark also lets users send and receive payments and transfers across ASPs "atomically" through the Lightning nodes run by ASPs, without bearing the burden of running a node themselves. This should vastly improve on Lightning's weakness in reliability and dramatically reduce failure rates. Being able to receive without keeping anything running is another great advantage.
Of course, users do bear a liveness requirement. It's true that anyone who wants a fully unilateral exit needs to be fairly diligent about maintaining that liveness. But only those who want that need to do so.
In conclusion, I believe Ark can be called self-custodial when used with a precise understanding of how it works, and I expect that, thanks to its overwhelming convenience, it will play the most important role if a world where people pay with bitcoin ever arrives.
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