The TYPO3 Core Team releases LTS-versions (long-term support) every 1.5 years. These versions are actively maintained and supported for 18 months and receive security fixes and critical updates for an additional 18 months. This results in a total of 3 years of free support by the TYPO3 community.
This is a companion discussion topic for the original entry at https://typo3.org/article/x-marks-the-spot-typo3-v10-0-is-here