The reason we are not calling it Opus 2 is that it could confuse some people into thinking we broke compatibility. Opus 1.3 is perfectly compatible with Opus 1.0, and all future releases will keep that compatibility.

And in this conversation lies a great example of why semantic versioning != romantic versioning.

Good read: http://dafoster.net/articles/2015/03/14/semantic-versioning-...

What design decisions went into the spec that has allowed you to maintain compatibility for so long?

If you could break compatibility, what would you change and why?

Like many other audio codecs, Opus lets the encoder decide how to spend the bits is has -- on what frame and on what frequency bands. On top of that is has a few special features that also require decisions from the encoder. So while the decoder doesn't change, the encoder can be improved to make better decisions. While the format itself is not perfect, I have not come across any particular thing that would be worth breaking compatibility over. I prefer working within the constraints of the bitstream to keep improving the quality.