Running the new system in parallel costs a few weeks and eliminates the category of failure that kills automation programs.
Automation programs rarely die from bad code. They die from one visible failure in the first month that costs leadership its confidence. Shadow mode is how you spend three weeks to prevent that.
What shadow mode means precisely
The new system processes every real case and records what it would have done. Humans continue doing the work. Nightly, you compare outputs and classify every divergence: system correct, human correct, or ambiguous.
The third bucket is the valuable one. Ambiguity almost always reveals an undocumented rule.
Set the threshold before you look at the data
Agree the accuracy and cost thresholds for cutover in writing, in advance, with the business owner. Deciding afterwards turns an engineering judgment into a negotiation.
Cut over by segment
Then move one segment, category, or region at a time, with a rollback procedure documented and tested. Every engagement we have run this way has held its rollout schedule. The ones that skipped it are the ones we cite in this article.