With the growing popularity and prevalence of Drupal 8, it should come as no surprise that many Drupal development companies are slowly edging away from supporting earlier versions.
Since February 2016, Drupal.org, the flagship of the Drupal development community, itself ceased offering support for Drupal 6 (and, naturally, anything earlier).
This Drupal 6 departure is widely reflected in the wider Drupal community, where no bug fixes, documentation or new projects have been tabled for over nine months. Significantly, there have not been any security advisories for Drupal 6, either.
Since this Drupal.org decision, and in a move that both re-states their commitment to their clients, and dedication to Drupal, Acquia has continued to offer their own support for Drupal.
This commitment to clients with the earlier Drupal platform, has ensured that Acquia Cloud supports Drupal 6 sites, an important issue to both Acquia, as well as partners such as Appnovation.
After extending this support far beyond many in the Drupal development community, Acquia has recently announced that, as of the end of February 2017, they will finally be ending their regular support for Drupal 6 sites.
To enable continued support for clients that still need or want it, however, Acquia is offering a D6 Extended Support Package, with various options available depending on the nature of individual client needs.
As Drupal 8 becomes more popular, the overall support available for Drupal 6, while still being available, is certainly likely to become more sporadic, as the Drupal community focuses on perfecting Drupal 8.