GoogleSystemConfirmedHigh impact
Penguin 4.0 (real-time, into core)
Penguin became part of the core algorithm, ran in real time and moved from demoting sites to devaluing spammy links.
What changed
Google announced that Penguin now operated continuously within core ranking, so changes were reflected as pages were recrawled rather than waiting for a refresh. It also became more granular, adjusting rankings for affected sections rather than whole sites, and Google said it now discounted spam links rather than penalising the target. Google stopped announcing Penguin updates from this point.
Timing
Rollout began 23 September 2016. No completion date was announced. Rankings typically remain unstable for the whole rollout window, so measurements taken inside it are not a reliable read on the outcome.