[niftich]

So based on their github and some searching with google, historically they didn't have much of an end-of-life policy, because there were no bugfix releases for v1.x.x after v2 came out, and no bugfix releases for v2.x.x after v3 came out:

v3.0.0 - 2013-08-19

v3.0.0 RC1 - 2013-07-27

v2.3.2 - 2013-07-27

v2.3.1 - 2013-03-01

v2.0.0 - 2012-01-31

v1.4.0 - 2011-11-03

v1.3.0 - 2011-09-16

With major version 4 still being in alpha, there are concurrent releases of 3 going on still, but based on their previous releases, I don't expect a v3 bugfix release after 4.0.0.

[yRetsyM]

They mention in the original alpha release article this was a mistake. They plan on supporting and bug fixing for the foreseeable future with bootstrap3

http://blog.getbootstrap.com/2015/08/19/bootstrap-4-alpha/

[niftich]

An update over the course of the previous 19 hours [1][2]; apparently that foreseeable future ended 10 hours after you posted this excellent reminder. They have begun closing [3] all outstanding github issues for v3 with the text:

  Bootstrap 3 is no longer being officially developed
  or supported.

  All work has moved onto our next major release, v4.
  As such, this issue or pull request is being closed
  as a "won't fix." For additional help and support,
  we recommend utilizing our community resources.
  Thanks for your understanding, and see you on the
  other side of v4!

  <3,
  @mdo and team

[1] https://github.com/twbs/bootstrap/issues/20631

[2] https://news.ycombinator.com/item?id=12435425

[3] https://github.com/twbs/bootstrap/issues/16913