This page aims to cover in brief the history of the K dialects and their official implementations.
The original K specification
K2 and K3
K2 and K3 were the first commercially developed and supported versions of K made at Kx Systems. K3 came with a complete reference manual that consisted of the documentation for the entire language. kdb+ was a database system that was sold along with K that provided an in-memory database manageable using K.
K4 was released in 200. In 2003, along with K4, Q was released as a "wrapper around k providing readability". K4 is the current commercial dialect supported by Kx Systems, which is bundled alongside Q as an implementation language. K4 requires a command to switch from Q to K, and the documentation at code.kx.com does not cover K4.
Arthur Whitney sold his majority stake in KX systems in 2018 and departed along with a few of his associates to create a new company called Shakti, along with which came the creation and development of the K7 and K9 dialects.
K7 was maintained for a few years and is no longer available for use.
K9 is currently nascent and (as per onsite claims) supports fast processing of tables with row numbers in the billions and trillions. Binaries for K9 are available at shakti.com.