Google SEO
2018–2020 — Google Search Central Blog
How did Google phase in mobile-first indexing?
Google moved websites in stages, notifying owners through Search Console rather than switching the entire web at once. The transition was completed in 2023.
Further analysis
Use this entry as an audit checkpoint. The cited source establishes the context; the direct answer identifies what to check before choosing an action.
In SFT, this topic relates to Structure. Check whether the signal is visible on the page, connected to the rest of the website and supported by understandable evidence.
Related search terms include mobile-first waves, gradual migration. Use them to describe the issue in a brief, audit or answer page.
Applying SFT
Structure turns a rule into readable architecture: headings, URLs, structured data, visible content and clear hierarchy.