Drupal 10 will be supported until the release of Drupal 12 in mid-late 2026
New major release schedule

Beginning with Drupal 10, a new Drupal major version will be released every two years in even years (2022, 2024, etc.). 
Each major version will receive active support for about two years, followed by maintenance support and security coverage for about two more years. Each is supported until two more major versions have been released.

Drupal 11 will be released in 2024

Drupal 11 will be released sometime in 2024. 
Like Drupal 9.0 and 10.0, Drupal 11.0 has three potential release windows, in June, August, and December. 
The window used will depend on when the beta requirements are complete. 
For more information, refer to the Drupal core release schedule.

Drupal 11 alpha development opens this week

Following the release of 10.2.0-beta1, changes to 11.x that diverge from Drupal 10 under the continuous upgrade path will begin. 
Anyone can get involved in completing the requirements for Drupal 11. 
Join the #d11readiness channel in the Drupal community Slack.

Maintenance minor versions of Drupal 10

Following the release of Drupal 11.0.0 in 2024, a long-term support phase for Drupal 10 begins, and it will include a new maintenance minor every six months. 
Each maintenance minor will contain a limited set of changes backported from Drupal 11. 
For more information, refer to the Drupal core release process overview.

Use a supported PHP version for the best ongoing support

Maintenance minor releases for Drupal 10 will keep adding support for newer PHP versions as they are released. 
The minimum supported PHP version for Drupal core follows the PHP core team's support cycle. 
(Reference: What does it mean for a PHP version to be supported?)

Site owners wishing to take advantage of Drupal 10's long-term support phase should ensure their platforms always use PHP versions supported by the PHP maintainers.

Announcement written in collaboration by Dave Long, Jess (xjm), Nathaniel Catchpole and Victoria Spagnolo.
 

Upgrade Status

Use to prepare for a Drupal 9 to 10 upgrade or Drupal 8 to 9 upgrade#

The 4.x version of this module provides all-around support for preparing for your upgrade to Drupal 10 from Drupal 9, while 3.x does the same for Drupal 8 to Drupal 9. It is not possible to directly upgrade from Drupal 8 to Drupal 10.

install the upgrade status module, and review how difficult it will be to upgrade to drupal 10