Apple Inc. is expecting huge demand for its next smartphone. The company has requested that its suppliers manufacture between 85 million and 90 million units of the so-called iPhone 6S by the end of 2015, unnamed sources told the Wall Street Journal.

That order encompasses both the 4.7-inch and 5.5-inch variants of the coming iPhone. In contrast, Apple ordered between 70 million and 80 million units of its iPhone 6 and iPhone 6 Plus last year, the Journal previously reported. Even with such a large order, both models quickly sold out in the wake of their September launch, remaining in short supply until the Christmas holiday season.

Apple’s introduction of the iPhone 6 and iPhone 6 Plus came well behind new Android models marketed by HTC Corp., LG Electronics Inc. and Samsung Electronics Co. Ltd. But their launch has paid off big, with 135.6 million iPhones sold in the first half of its fiscal year, according to Apple quarterly financial data.

At first glance, the difference between the iPhone 6 and the iPhone 6S may not be too pronounced. The shell of the new smartphone is expected to be nearly identical to its predecessor, according to leaked images obtained by 9to5Mac. Many of the changes may be more internal than external, beginning with a new processor, an improved camera and increased RAM.

The one readily apparent change is a Force Touch display on the iPhone 6S. The technology allows a touch pad or touch screen to detect the difference between a light tap and a hard press. This can be used to enable new controls and gestures, such as a contextual menu that pops up on a hard press. Apple first introduced Force Touch with the Apple Watch and its redesigned MacBook.

Apple is also considering a third assembler -- Wistron Corp. -- to complement Foxconn Technology Group and Pegatron Corp. in putting together the iPhone 6S, according to the Wall Street Journal. It’s not uncommon for the company to employ multiple vendors in building its products, and it tapped Wistron in building the plastic iPhone 5C, released in 2013.

Apple hasn’t officially announced the iPhone 6S, but if the company follows its release trend in recent years, the smartphone may be announced in September and sold in stores shortly thereafter.

The company is expected to issue its financial report for the third quarter of its fiscal year July 21. Consensus Wall Street estimates expect the firm to report at least 50 million handset units sold in the three-month period ending June 30.