Every paid response from these services is Ed25519-signed and carries an evidence record stating what was checked and what the answer does not establish. This page verifies the signature in your browser and renders that record. Nothing is sent anywhere.
The token is a compact JWS. This page decodes the header to read the key id, fetches that service's published key from its /.well-known/signing-key.json, and verifies the Ed25519 signature using the browser's own WebCrypto — the same primitive, running on your machine, with no trust in this page beyond the code you can read with View Source.
If the key id in the token does not match the currently published key, the signature will fail even if it was valid when issued. That is the correct behaviour and it is why the keys are pinned rather than regenerated.