Shadow first, then Handover.
How service moves from a lender's current process to the model, and back if the evidence turns.
Three states, one book
Before Handover, three things run side by side on the lender's book: the current process, which keeps serving; zypl.Foundation, scoring in shadow; and the lender's held-out outcomes, which are scored and kept for review. Nothing in that arrangement changes a decision.
What moves service
Service moves when the lender's own held-out outcomes show the model ranks better, the validator has reviewed the pack, and the risk owner signs. Until then the model scores in shadow. If the evidence turns, service moves back to the current process.
- The outcomes are the lender's. They are measured on its own book, held out from what the model sees.
- The pack is the validator's. It is reviewed before the decision, not after it.
- The signature is the risk owner's. No threshold moves service on its own.
In replay
In replay on 10 private books, automatic Handover lifted served AUC from 0.651 to 0.699, recovering 70% of the hindsight gap (63% on the 7 books unseen in training).
Why the sign-off stays with the lender
A research result can say where to look. It cannot say that a model ranks one particular book better; that has to come from the book. Handover is the step where the lender's own evidence decides, and where it can decide the other way.