Considering the current numbering scheme, 0.9 will be the unstable version of 1.0. Which means 0.9 should give us a very good idea of the final backwards compatible API (hopefully)
The dots are there for a reason.
major.minor.revision
minor is incremented when backwards compatible features are added
major is incremented when backwards incompatible change is introduced.
All of them are integers, and the smaller ones are reset to 0 when a bigger one is incremented.
For versions 0.x.x (pre v1), backwards incompatible changes are allowed at any time.
There are more rules, see http://semver.org/