It builds off of several specifications that came from the crypto crowd. It does not use a proof of stake or proof of work blockchain, though, so depending on how you use the words "crypto" and "blockchain," it either is or is not those things.
> It builds off of several specifications that came from the crypto crowd. It does not use a proof of stake or proof of work blockchain, though, so depending on how you use the words "crypto" and "blockchain," it either is or is not those things.
From the protocol's FAQ docs itself:
> Is ATP a blockchain?
> No. ATP is a federated protocol. It's not a blockchain nor does it use a blockchain.
https://atproto.com/guides/faq#is-atp-a-blockchain
Architecturally, it's an attempt at improving ActivityPub in terms of account transfers & portability between federated instances, which ActivityPub doesn't inherently support. Mastodon, by comparison, requires one of those steps to be the explicit export into a locally-saved file, rather than communications between the federated instances themselves.