PubSubHubbub 0.4 brings many updates and enhancements.
Among them:
- Breaking change: “sync” mode of subscription verification has been removed.
Anf for information:
*hub.verify_token, permanent subscriptions and Hub-initiated subscription renewals have been also removed.*
from: https://groups.google.com/forum/#!msg/pubsubhubbub/7RPlYMds4RI/2mIHQTdV3aoJ
Answer: It makes no more difference now, just use async
as verify type.