The first developer preview for Android 10 went live in March last year. We expect the same release timeframe for Android 11 this year, and the fact that a Pixel 4 has been found running Android 11 on a benchmark supports that notion.
https://www.notebookcheck.net/Google-Pixel-4-caught-running-Android-11-ahead-of-Developer-Preview-1-release.450643.0.html