The world's top two smartphone-makers -- Samsung Electronics and Apple -- have been seeking to revive their lukewarm sales by introducing more diverse formats, with their next experiment being thinner models.

According to industry sources Tuesday, Samsung is expected to add a thinner model, tentatively called Slim, to its flagship Galaxy S25 lineup to come out next month.

While Samsung remains mum over the exact specifications of the new phones, rumors say that the Slim could come in at about 6 millimeters in thickness, which compares to 7.6 mm for the Galaxy S24 and 8 mm for the iPhone 16 -- the two respective latest models.

So far, the thinnest Galaxy S model to date was the Galaxy S6, released in 2015, which measured 6.8 mm. Among all Galaxy devices, the slimmest remains the Galaxy Alpha, also launched in 2015, at 6.7 mm.

Other features of the Slim include a 200-megapixel main camera, similar to the Galaxy S24, and a 6.7-inch Dynamic AMOLED display. Reports also suggest it will have a battery capacity between 4,700 and 5,000 milliampere-hours. But nothing has been confirmed yet.

In the meantime, Apple is also gearing up for its thinnest smartphone. Jeff Pu, an analyst at Haitong International Securities, projected in a recent report that the upcoming "iPhone 17 Air" will measure just 6 mm thick and include a 6.6-inch display.

But the slimmer iPhone is rumored to come with a single, less advanced 48-megapixel camera, compared to the cameras for Apple's flaship models.

The iPhone 17 Air has reportedly entered Foxconn's new product introduction stage, indicating production preparations are underway. The device is slated for release in late 2025, making it Apple’s slimmest smartphone.

Samsung's Slim is expected to debut later next month together with other flagship S25 models. Sources say the initial shipment would remain at about 3 million units to gauge the market reaction to the slimmer model.

During Samsung’s third-quarter earnings conference call, Daniel Araujo, corporate vice president for Samsung's mobile experience division, stressed the tech giant’s focus on enhancing real-world artificial intelligence experiences with the upcoming Galaxy S25 series.

“We aim to lead innovation in everyday life with the next-generation Galaxy experience,” he said.

Amid the heated race to introduce slimmer phones among smartphone rivals, also including China's Huawei, sources remained cautious about durability issues.

"The format competition between Samsung and Apple is expected to continue intensifying until they reach the limit. But the key challenge remains in ensuring their durability while effectively controlling overheating issues," an industry source said on condition of anonymity.

By Jie Ye-eun (yeeun@heraldcorp.com)