Axelar Amplifier and verifier sets

Axelar is a Cosmos SDK chain whose entire job is cross-chain routing. The validator set signs off on messages crossing the hub, which lets Axelar act as a general message passing layer with a single unified security assumption.

Amplifier is the newer architecture that opens the model up: external chains can be added permissionlessly, with their own verifier sets running as CosmWasm contracts on the Axelar chain. That means a new rollup can integrate by writing a verifier in Rust and deploying it, rather than negotiating an integration with the core team.

The hub-and-spoke model trades some direct-pair efficiency for simplicity: one integration gets you every connected chain, not just one counterparty.