Apple Inc.'s (AAPL - Get Report) iPhone 8 appears to be off to a rocky start since going on sale last month. 

The iPhone 8 models represented just 16% of total U.S. iPhone sales during the fiscal third quarter, with the iPhone 8 at 6% and the iPhone 8 Plus at 10%, according to a survey of 500 Apple customers in the U.S. conducted by Consumer Intelligence Research Partners (CIRP). Those numbers pale in comparison to when the iPhone 7/7 Plus went on sale last year, with both models capturing 43% of sales, according to CIRP. Further, when the iPhone 6/6 Plus launched in 2015, the phones represented 46% of all iPhone sales during the quarter. 

"In terms of consumer demand and reception, the 8 and 8 Plus have a share of total sales that makes them look much more like an 'S' model, while the 7 and 7 Plus was close to the very well-received 6 and 6 Plus," said CIRP analyst Josh Lowitz. "This is not surprising, as the form factor remained the same, and the improvements in features were incremental and internal." 

Separately, data from mobile app analytics company Localytics shows that the iPhone 8 and 8 Plus only have 2.4% of the total iPhone market share. iPhone 8 Plus adoption appears to be tracking more in line with the iPhone 7 Plus, Localytics noted, while iPhone 8 adoption is showing "significant decline." 

"This is decent growth for the iPhone 8 Plus, as it has jumped from 0.4% market share after the first weekend of sales to 1.4%," the company said. "This is a similar trajectory to what we saw with last year's iPhone 7 Plus. However, growth for the iPhone 8 continues to be a challenge for Apple, with a meager 0.71 [percentage point] increase between the first weekend and the first month of sales." 

Apple products.
Apple products.

Analysts and investors have been trying to gauge consumer sentiment for the iPhone 8 models ahead of the release of their pricier, more high-end cousin, the iPhone X. The 10th anniversary edition of Apple's flagship device, which starts at $999, will become available for pre-order starting on Friday, Oct. 27. It's expected to ship on Nov. 3, though the iPhone X is likely to be in short supply, as Apple has struggled to ramp up production of the phone's advanced components, especially the facial recognition technology. 

Numerous data points have suggested that consumers may be holding off on buying an iPhone 8/8 Plus in favor of the iPhone X. A recent RBC Capital Markets survey of more 4,000 iPhone buyers found that 28% of respondents plan on purchasing the iPhone X. About 17% said they want to buy an iPhone 8, while 20% intend on purchasing an iPhone 8 Plus. 

The iPhone X represents one of the biggest form factor changes for blockbuster device in several years. By comparison, the $699 iPhone 8 and $799 iPhone 8 Plus offer fewer noticeable changes, aside from wireless charging, a faster processor and improved cameras. 

CIRP analysts expect weak iPhone 8 sales to impact Apple's fiscal fourth-quarter results on Nov. 2, according to the Wall Street Journal. That's likely to increase the pressure for Apple to deliver blockbuster results with the iPhone X. 

Others have noted that Apple's fiscal third and fourth quarters might produce in line results, rather than being blowout quarters. Once the iPhone X starts selling, its sales are more likely to show up in Apple's fiscal first or second quarter, at which point it could lead to record-breaking results.

All that depends, however, on whether analysts are correct that consumers are interested in purchasing the iPhone X.

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