Safari 27.1 adds foldable-aware web features for iPhone Duo

Safari 27.1 on iPhone Duo automatically shows PDFs as two pages when the device is partially folded. Developer previews of the Device Posture API and Viewport Segments API let sites adapt to the foldable display.

• PDFs render as two pages when iPhone Duo is partially folded
• Device Posture API reports folded and continuous states
• Viewport Segments API exposes segment sizes and positions
• Both APIs ship as developer previews behind Safari flags