The Zabbix versioning scheme has changed a few times over the years. In general, the first two numbers have denoted a major version, such as 2.4, 3.0 and 4.0, while the third number has denoted a minor version number. Previously, an even second number denoted a stable branch, while an odd second number denoted a development branch. Hence, 2.3 was a development branch for 2.4, while 2.4 was the resulting stable branch. This has slightly changed since 3.0. The development releases have moved away from the odd numbering, that is, the 3.5 number. They're now called 4.0.0alpha1, 4.0.0beta2, and so on. This is deemed to be more user friendly, although the internal numbering is still based on 3.5 in several places—the database version, for example, which we'll explore in more detail a bit later.

The new version numbering since Zabbix 3.0 could be summed up as follows:

• A version number with just digits (and dots) in it denotes a stable release
• A version number with the alpha, beta, or rc (release candidate) keywords added isn't a stable release