The Duo opens like a book, from a 5.4-inch outer display to a 7.6-inch inner one. It runs on the A20 Pro processor with iOS 27.1 and starts at $1,999 in the U.S. and £1,999 in the U.K., about $700 more than the iPhone 18 Pro Max. Preorders opened October 16. The launch covered more than 70 countries, and 28 more markets are listed for October 30.

Macworld attributed the delivery delay to supply constraints and reported low production yields. Creative Bloq reported that the phone was sold out until January and that some customers had been told they would wait until then for replacements.

Most of the early complaints are about durability. Reports describe cracks along the fold of the inner display and trouble with the hinge. Creative Bloq listed vertical cracks around the hinge, dead pixels and lines across the screen. On October 23, Apple published troubleshooting guidance saying cases that cannot be resolved may require replacing the inner display assembly.

The two outlets disagree on how serious the problem is. Creative Bloq said there is no evidence of a widespread manufacturing defect and expects software fixes as developers catch up. Macworld said the cause and scale of the problem remain unclear.

Independent fold tests have measured how the crease changes over time. Testing by Tim Pan found it became visibly deeper after 500 manual folds and could be felt as deeper after 10,000. HTX Studio found the Duo's crease deeper than those of two other foldables after 3,000 folds, and noted that the screen around the crease is softer.

Heat has drawn complaints too. Joanna Stern ended a FaceTime call on the Duo because the device felt too hot. Apple said the warmth shows that the vapor chamber and flexible graphite heat pipe are working correctly to move heat away.

Software on the larger screen is uneven. According to Creative Bloq, some apps on iOS 26 or 27 show black bars on the inner display or appear as tiny, blurry versions of themselves. Other reported bugs include faulty transition animations and wrong camera orientation. Reviewers have also noted that app optimization varies.

The Duo has two 48MP rear cameras, an under-display FaceTime camera, a dual-battery system and multitasking features including Split View. Apple Pencil support is due later this year. Unlike other iPhone models, it has no dedicated telephoto camera, no variable aperture and no Action button. It also uses Touch ID on the side button instead of Face ID, which Stefan Van Der Merwe called a "deal breaker."