There is not a unstable then a stable phase, but 3 phases:

1. the API is unstable as hell
2. the API is mostly settled
3. In the third phase, the API is fully stable, and no backwards-incompatible changes are expected.

We can name these:

• experimental (unstable)
• production-ready (still unstable, but you can budget-in a bounded amount of upgrade work)
• stable (no maintenance work is required)