The iPhone 4S (retroactively stylized with a lowercase 's' as iPhone 4s as of September 2013^[7]) is a smartphone that was designed and marketed by Apple Inc. It is the fifth generation of the iPhone,^[8] succeeding the iPhone 4 and preceding the iPhone 5. Announced on October 4, 2011 at Apple's Cupertino campus,^[9] its media coverage was accompanied by the death of former Apple CEO and co-founder Steve Jobs on the following day.

Available for pre-order on October 7 and coming to mainstream availability in retail stores on October 14 in the United States,Australia, Canada, the United Kingdom, France, Germany, and Japan, sales peaked over its predecessor with over a million sales in the first twenty-four hours of preorder availability and over four million sales in the first four days of retail availability. Further worldwide rollout, including 22 additional countries on October 28, came over the next several months.^[10]

This iPhone was named "4S" where "S" stood for Siri (Apple CEO Tim Cook confirmed that during the Q&A session at the D10 conference in May 2012^[11][12]), an iPhone 4S-exclusive intelligent personal assistant that was later included in future generations of mobile Apple products. Retaining the external design of the iPhone 4, the 4S hosted revised hardware specifications, most notably an upgrade to the Apple A5 chipset, and an 8-megapixel camera with 1080p video recording. It debuted with iOS 5, the fifth major version of iOS, Apple's mobile operating system, that introduced features including iCloud, iMessage, Notification Center, Reminders, and Twitter integration.

Reception to the iPhone 4S was generally favorable. Reviewers noted Siri, the new camera, and processing speeds as significant advantages over the prior model.^[13][14][15] It was succeeded by the iPhone 5 as Apple's flagship phone on September 12, 2012. The iPhone 4S remained in production, albeit being sold with reduced storage (from 16/32/64 GB down to 8 GB.) It was officially discontinued on September 9, 2014 following the announcement of the iPhone 6 but is currently supported as of iOS 9: so the iPhone 4S is the first iPhone to support five major versions of iOS: these being iOS 5, 6, 7, 8, and 9.

As early as May 2011, some leaks had a fairly accurate description of the iPhone 4S including the name "iPhone 4S", the Apple A5chip, HSDPA,^[16] new camera, and Sprint carrying.^[17]

The iPhone 4S was unveiled at Apple's "Let's Talk iPhone" event on October 4, 2011, on the Apple Campus in Cupertino, California.^[18] The keynote was the first which Tim Cook gave since the Verizon keynote earlier in the year. It was also Cook's first launch without Apple co-founder Steve Jobs, whose health was deteriorating, and who died the day after the announcement of theiPhone 4S. Tim Carmody of Wired praised Cook for focusing on company achievements, calling him a "global business thinker" and a "taskmaster".^[19]

At the "Let's Talk iPhone" event held by Apple on October 4, 2011, Mike Capps demonstrated Epic Games' Infinity Blade II, the sequel to Infinity Blade, on an iPhone 4S. Capps boasted that the game uses Epic Games' Unreal Engine 3 and features the same graphic techniques used in the Xbox 360 game Gears of War 3.^[20]

Speculation about Apple's next generation phone, including various specifications and a predicted name "iPhone 5", had been widespread in the time preceding its debut.^[21] After the iPhone 4S was announced, it was considered by some media to be a disappointment, due to the expected release of an iPhone 5.^[21][22]

There were no external differences between the iPhone 4 CDMA model and the iPhone 4S, with the exception of a SIM card slot on the iPhone 4S.^[21] All changes were internal (slight external differences between the iPhone 4 GSM model and the iPhone 4Sexist, as said differences existed between the CDMA and GSM models of the iPhone 4).^[23][24]

On September 10, 2013 the iPhone 4S name was re-stylised as iPhone 4s, using a lower case 's' to reflect the names of the newly announced iPhone 5S and iPhone 5C. This was unusual for Apple as an upper case 'S' had been used since the introduction of the iPhone 3GS in 2009.^[25]

On September 9, 2014, the iPhone 4S was discontinued following the reveal of the iPhone 6 and the iPhone 6 Plus.^[26]