How long do you expect?

Java 7 had less than four years of support.

Ubuntu Desktop LTS was three years, and starting with 12.04 it increased to five years.

That's a language runtime and an operation system known for their stability, forming the bottom of very wide and deep ecosystems.

Show me a web framework with a 3 year LTS, and I'm overjoyed.

Symfony has 3 year LTS plus a year security support after. http://symfony.com/doc/current/contributing/community/releas...

Well the new model will have a new LTS every 2 years, with guaranteed compatibility as long as you didn't have any deprecation warnings. So you get 2 years to fix warnings, then a guaranteed working new version. I find it hard to believe anybody is doing anything better in this space.

If you start your project on the day a LTS comes out, you'll theoretically be compatible with the _next_ LTS, 2 years later, so in some ways it's up to 5 years until you need to change your code.

Django releases tend to add useful features/optimizations, and have very light upgrade effort. Most devs will WANT to upgrade to the latest stable.