Last Quarter Was Quiet

You are setting an availability SLO for the first time. Last quarter measured 99.97 percent, so a staff engineer proposes 99.97 percent as the target: it is proven achievable and nobody can argue with it. Two facts sit in the same document. Last quarter included a six week feature freeze during a compliance audit, and the largest customer's own promise to their users is 99.5 percent. What should the SLO be derived from?

99.5 percent, matching the largest customer's own promise so you are never the reason they breach

What users need and what the business will pay to keep, checked afterwards against measured performance to see whether it is reachable

99.97 percent, since it is measured, defensible and gives an honest budget from day one

99.99 percent, because a target the team has not hit yet is what drives reliability work