Yes — CallKit will return callUUIDAlreadyExists on the second report, which suppresses the second ring. However, on iOS 16+ we observed that the duplicate reportNewIncomingCall still produces a brief banner flash (~80–120 ms on A13-class silicon) before CallKit rejects it. On newer silicon the flash is imperceptible but a subtle haptic tick still plays. To make the duplicate report truly invisible, three things together: Deterministic UUID derivation from the call ID (SHA-256), so both transport paths converge on the same UUID without any coordination. A phantom CXCallUpdate with empty caller info on the duplicate path — if the race slips through, what flashes is an empty card, not "Unknown". Immediately in the completion block, a historical end: reportCall(with: uuid, endedAt: Date(timeIntervalSinceNow: -3600), reason: .answeredElsewhere) The .answeredElsewhere + historical endedAt combination is the only end reason we found that CallKit dismisses with zero transient UI — no flash, no haptic, no Missed entry in Recents. We tried .remoteEnded, .failed, .declinedElsewhere, and .unanswered — each has a visible or audible side-effect. Full writeup with drop-in Swift code, reproduction guide, and the full list of alternatives we tried and rejected: https://github.com/sefatanis/ios-callkit-duplicate-ring-suppression Tested on iOS 14.8 – 18.1.