June 2019 core update
First core update Google pre-announced, giving publishers a day's notice before the rollout began.
What changed
Google announced on 2 June 2019 that a broad core update would launch the next day, the first time it had given advance notice. News publishers reported significant swings, and Google separately released a site diversity change in the same week, which complicated attribution. Google published a detailed blog post on what site owners should know about core updates shortly afterwards, which remains the canonical guidance.
Timing
Announced on 2 June 2019, with rollout beginning 3 June 2019. 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.