According to Canonical's blog post, Ubuntu 14.04 LTS (the latest LTS release with Upstart by default) will be supported until April 2026, Ubuntu 16.04 - the last official release with Unity 7 as the default desktop environment - until 2028, Ubuntu 18.04 (the latest LTS release with support for 32-bit architecture) - until 2030, Ubuntu 20.04 - the latest release with the Firefox package in the central repository - until 2032. In total, 6 LTS releases will be supported simultaneously.
A Canonical account is required to receive support for 12 years instead of five. It provides access to a subscription for 5 machines.
The change will affect all LTS releases of Ubuntu, including the upcoming release of Ubuntu 24.04, which will be supported until 2036.
For comparison: Red Hat Enterprise Linux has a support life of 14 years (3 distributions are supported simultaneously), Red Hat Enterprise Linux clones have a support life of 10 years (2 distributions simultaneously), 13 years for Suse Enterprise Linux (3 distributions simultaneously) and 7 years for Debian (3 distributions). The support period is 5 years for CentOS Stream (two, support for the 8th will soon end), Alt Linux SP (one - the 8th) and RedOS (two, support for the 7th will soon end).
Source: linux.org.ru