Ah, I think it's changed to https://api.opencorporates.com/reconcile and indeed it now requires an API key (where in their OpenRefine Reconciliation API docs, it says it does not, but might change in the future.)
And indeed they did change that policy,
An API token is required to access the OpenCorporates Reconciliation API.
and so they now require an account to be setup and then an API token (key) will be given depending on your application but given only X requests per day unless you pay for higher usage with a paid-for API account. Makes sense.