Why Is Forward Compatibility Such a High Priority?

It seems like there is a lot of effort (maybe not a lot, but some) spent on making sure, for example, that a .blend file made in a 2.6x file will open in 2.5x. That doesn’t really make sense to me. The other way definitely does, and I hope Blender keeps that. Does anyone know the rationale behind this?

Thanks in advance!

Believe it or not, the past several years have seen a small number of people still using 2.49 as their main version, now those that do would want to try to make sure that they can backport 2.6x models to 2.4x.

However, such extreme forward compatibility, I would say is not of utmost priority in some cases, a number of files in the latest versions for example would likely break in 2.5x due to overhauls like Bmesh and backporting to 2.49 now will likely result in a loss of data even though the scene will open.

So yes, the BF tries to make sure there is some flexibility in which version you open a scene in, but they’re aware that they can’t support forwards compatibility to very old versions forever.

It seems like there is a lot of effort (maybe not a lot, but some) spent on making sure, for example, that a .blend file made in a 2.6x file will open in 2.5x
Is there ?

Things broke going from 2.4x to 2.5x (for example changes to the animation system meant some animations made in 2.5+ won’t work in 2.4x)

Ton also mentions that compatibility can break in the 2.7 series http://code.blender.org/index.php/2013/06/blender-roadmap-2-7-2-8-and-beyond/

For 2.7x projects we will allow forward and (minor) backward compatibility breakage. That means that by default, the 2.7x .blend files don’t have to read reliably in 2.6x or older.

The “x” is what it’s about. The “minor” version changes 2.4->2.5->2.6 usually are considered major steps, where breakage is allowed if necessary. Compatibility should be preserved during each of these versions, i.e. when the “x” changes (2.68<->2.69 should be compatible).