iOS 26.4 RC drops

Apple seeded the iOS 26.4 RC as build 23E244 on March 18, 2026, and posted an Xcode 26.4 RC (17E192) the same day on the Apple Developer site. (developer.apple.com) The release notes flag a reproducible hang: Address Sanitizer and Thread Sanitizer may hang on macOS 26.4, iOS 26.4, tvOS 26.4, watchOS 26.4, and visionOS 26.4 when building with Xcode 26.3 or older, and Apple’s recommended workaround is to use Xcode 26.4. (developer.apple.com) Background Assets gained three developer-facing APIs: localStatus(ofAssetPackWithID:) returns full status offline, assetPackIsAvailableLocally(withID:) returns a synchronous Boolean, and ensureLocalAvailability(of:requireLatestVersion:) accepts shouldUpdate=true to force the latest pack to be stored locally. (developer.apple.com) Applications can now opt in to full Memory Integrity Enforcement (MIE) protections rather than the previous Soft Mode, an opt-in change tracked in the release notes under issue 160719439. (developer.apple.com) The Messages beta surface shows RCS end‑to‑end encryption exposed for cross‑platform testing between Apple and Android devices but Apple notes the feature is not shipping in this release and is dependent on device and carrier support. (developer.apple.com) Developer-facing highlights in coverage of the RC include Apple Music’s Playlist Playground, the 2026 emoji set, and a targeted keyboard bug fix, while Reality Composer for iOS retains a known issue that prevents exporting projects as.reality or USDZ in this beta. (macrumors.com, idropnews.com, developer.apple.com)