GoogleInfrastructureConfirmedHigh impact
Mobile-first indexing announced
Google announced it would begin using the mobile version of a page as the primary basis for indexing and ranking.
What changed
Google said that because most searches came from mobile devices, its index would move to using the mobile rendering of a page as the canonical version for indexing and ranking. It advised sites with separate mobile URLs or reduced mobile content that parity of content and structured data between versions would matter. Experimentation began immediately, with broad rollout starting in March 2018.
Timing
Rollout began 4 November 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.