XCUITest is the test harness Apple ships, reviews, and optimizes. It binds to the real accessibility tree, respects privacy entitlements, survives OS updates without bridge breakage, and — crucially — is the only UI automation framework whose output you can submit as evidence in an App Store appeal. Every alternative (Appium, Maestro, Detox) is a translation layer over XCUITest or a separate accessibility-service bridge. The translation layer is the thing that breaks first.
Anvil sits directly on XCUITest. KID — the Koydo iOS Driver — runs an NWListener server inside a development app-extension signed against your team. The extension wraps an XCUIApplication instance and exposes its verbs over a single JSON-RPC socket. No HTTP bridge, no gRPC, no capability negotiation. Eighty-two verbs, one wire.