ANSWER

What is an equivalence contract?

Reviewed October 22, 2026 · Reviewed by Paulo Pierrondi, founder.

An equivalence contract — the Equivalence Contract — is the written criterion for what must match between the legacy system and the replacement before cutover. It fixes fields, tolerances, blockers and the exceptions that may be approved with an owner, rationale and expiry. It is not a generic accuracy percentage: a small difference can be material while a large formatting difference may be irrelevant. During dual-run the legacy system stays in command and the replacement has no production effect. Cutover comes later, with human approval, a tested rollback and an Evidence Pack that records diffs, owners and the way back. Legacy Exit uses that contract to decide on proof, not on faith.

Step by step

• List outputs, critical fields and business rules to compare.
• Define tolerance by field and risk class, not one global percentage.
• Pre-classify blockers, material differences and cosmetic differences.
• Name an owner, rationale and expiry for every approved exception.
• Close the contract before dual-run: approvers, minimum evidence and tested rollback.

How an agent does this

At AgenticosCore, the Equivalence Contract guides Parallel. Every comparison and exception enters the Trail; House Rules prevent progression outside the criteria; and Brake keeps rollback operationally accessible. An approved exception enters the Evidence Pack with an owner, rationale and expiry. The Equivalence Contract is at /en/resources/equivalence-contract/.