✓Users cannot tell it from 99.99% through their own networks, and it leaves no budget for changesCorrect
✗ SLAs forbid it
✗ 100% is impossible to compute over a month
Why
A user on mobile data sees far more failures from their own connection than from a 99.99% service. A 100% target makes every deploy, failover and experiment a violation, so the team either stops shipping or ignores the SLO. Pick the lowest target users are happy with.