Apple's big iPhone launch event is less than a month away and new details have surfaced about what the tech giant may have in store for the next iteration of its flagship device.

Chief among the latest details is that Apple is calling this year's lineup an 'S year' - meaning that the new devices will mostly include internal improvements, instead of any major aesthetic overhauls, Bloomberg reported.

The report falls in line with widely reported rumours that Apple will launch three new iPhones on September 12.

The device maker is expected to release 5.8-inch, 6.1-inch and 6.5-inch models, all with edge-to-edge displays that are akin to the iPhone X.

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A 6.5-inch iPhone, referred to internally as D33, will feature Apple's largest screen yet, as well as new features like the ability to view content in a side-by-side view.

While it will be the biggest phone in the lineup, Apple is said to be mulling whether or not it should drop the 'Plus' label for the 6.5-inch device, Bloomberg noted.

The 6.5-inch and 5.8-inch models will both feature improved processing speed and upgraded cameras. It's unclear what specific changes will be made.

Apple will try to appeal to price-sensitive consumers with a 6.1-inch model that's most akin to the iPhone 8, aside from the addition of a bezel-less screen.

It will come in several colors, include an aluminum (rather than stainless steel) case, and feature a cheaper LCD display.

Since all three models will feature an edge-to-edge display, they'll also have the gesture-based control system used in the iPhone X, which replaces the need for a home button.

Face ID will also be included in all three devices.

Keeping with earlier rumours, Apple is expected to introduce dual SIM technology for the two larger phones in some regions, Bloomberg noted.

Including dual SIM support would allow users to switch between mobile carrier plans more easily.

It would also appeal to international users who often travel to multiple countries.

Another detail that remains unclear is what Apple will call the phones in its new lineup.

It's unlikely to brand the new premium phones as the iPhone Xs, as it could be read by consumers as 'excess' or 'extra small.'

The iPhone isn't the only Apple device expected to get a facelift at this year's event.

Apple is also expected to release an Apple Watch with a bigger screen, as well as revamped iPad Pro models that feature slimmer bezels, Bloomberg noted.

WHAT ARE THE 2018 iPHONE RUMOURS SO FAR?

Apple only launched the iPhone X a few months ago, but the latest rumours of its 2018 smartphone have already hit the web.

In August, rumours from the supply chain said the iPhone 9 will be available in two sizes, including one with a massive screen that would be Apple's biggest yet.

The 'Plus' size will reportedly have a 6.46-inch screen and will be sold alongside a smaller 5.85-inch model in a bid to compete with Samsung's Galaxy Note.

The leak came from a source within Samsung Display, the sole OLED supplier for the upcoming iPhones.

The source also said the smaller version was originally going to be a 5.28-inch model but that the firm upped it to 5.85 inches because of growing consumer demand for bigger-screen phones.

A recent Apple leak suggested the firm could cancel the iPhone X.

An analyst says the new model's disappointing sales could lead to the phone being cancelled - with production stopping as soon as this summer.

This could be the first time Apple has cancelled a phone model since the iPhone 5C in 2014.

Experts believe the lack of interest in the phone is largely due to the notch, which many potential Chinese customers believe removes too much space on the screen.

Now, Ming-Chi Kuo from KGI Securities says Apple will release three new iPhone models including a slightly cheaper 6.1-inch phone without 3D touch.

It could also release an updated iPhone X with a 5.8-inch OLED screen and a larger 6.5-inch OLED model, potentially called the iPhone X Plus.

The 6.1-inch phone will feature an aluminium frame similar to the iPhone 8 and the display will be an LCD panel instead of OLED, he predicted.

The 6.5-inch iPhone X Plus will have similar specifications as the current design but an OLED display and 4GB of RAM, he predicts.