Registry Basics: Versions and Stages

Why the registry exists

A logged model lives at runs:/<run_id>/model. That URI is fine for ad-hoc work but terrible for production: it changes every run and tells the serving layer nothing about which model is current.

The registry adds three things on top:

1. A named model (credit-scoring).
2. Versions (1, 2, 3, …) — append-only.
3. Stages per version (None, Staging, Production, Archived).

Serving and downstream pipelines now read a stable identifier:

models:/credit-scoring/Production

Promotion to a stage is the act that 'ships' a model — the registry is therefore the natural place to enforce review, sign-off and audit.

The registry is the hospital pharmacy for your models. Anyone can compound a drug in the lab (runs:/), but only drugs that pass the pharmacy's checks — batch number, expiry, signed-off by a pharmacist — leave on the medication trolley (Production).