From our initial analysis, the issue occurred due to an invalid automated quota update to our API management system which was distributed globally, causing external API requests to be rejected. To recover we bypassed the offending quota check, which allowed recovery in most regions within 2 hours. However, the quota policy database in us-central1 became overloaded, resulting in much longer recovery in that region. Several products had moderate residual impact (e.g. backlogs) for up to an hour after the primary issue was mitigated and a small number recovering after that.