The load forecast you built tells you what steady-state demand looks like: requests per second, model calls per request, human escalations per thousand sessions, cost per active user. The gate is the second document, and it exists to answer one question: what has to be true, measured over what window, for the opt-in flag to disappear?
Teams get this backwards. They decide they feel good about the feature, then hunt for numbers that support the decision. That produces thresholds that are either trivially met or impossible to meet, and neither one ends the opt-in period. A better method is mechanical. Take the forecast's steady-state line, add headroom for the failure mode you fear most, and write the number into the gate document.
Percentage-based rollouts are the standard mechanism for this transition. A cohort is selected by consistent hashing so the same user always lands in the same bucket, which keeps the experience stable across requests and keeps your measurement clean (OneUptime on percentage rollout flags). The rollout percentage is the physical lever. The gate document is the rule that says when the lever reaches 100.
One structural point before the numbers: the move from opt-in to default-on is a configuration change, not a deploy. That means your CI/CD pipeline may have no record of it. GrowthBook makes the point sharply: swapping a model ID or editing a prompt touches no codebase, so there is nothing for the pipeline to track or revert automatically (GrowthBook on feature flagging for AI models). If the promotion is invisible to version control, the gate document is your audit trail. Treat it that way.
Feature management platforms distinguish between gating release timing and gating commercial access, and the two use the same underlying flag machinery. Feature gates control what users see during a release; feature gating controls what a paying customer is entitled to after the release (Statsig on creating a feature gate, Schematic on feature gating in SaaS). Your promotion changes the release gate, not the entitlement. Keep those separate in the document or the review will drift into pricing questions.



