Audemars Piguet has replaced the long-running Calibre 2385 in its 38 mm Royal Oak Selfwinding Chronograph with the new in-house Calibre 6401. The update brings a 55-hour power reserve, a revised chronograph layout and, for the first time on this 38 mm chronograph, a sapphire display caseback. It is not the same movement as the 41 mm model’s Calibre 4401: Calibre 6401 is not a flyback chronograph.
What is the new calibre in the 38mm Audemars Piguet Royal Oak Chronograph?
It is Calibre 6401, an automatic chronograph movement developed entirely in-house, according to Audemars Piguet’s release account published by Europa Star. The movement replaces Calibre 2385, which the account says was introduced in 1997. AP’s official US product pages identify Calibre 6401 in both the steel and pink-gold 38 mm watches: steel reference 26450ST.OO.1356ST.01-B and pink-gold reference 26450OR.OO.1356OR.01-B.
The release account describes a five-year development. That marks a substantial mechanical change beneath an otherwise familiar 38 mm Royal Oak Chronograph format, rather than a new name for the former movement.
What changed with the new Royal Oak Chronograph 38mm?
A longer stated power reserve and faster beat rate
AP’s release account gives Calibre 6401 a 55-hour power reserve. Hodinkee reports the outgoing Calibre 2385’s reserve as 40 hours and lists the new calibre’s frequency as 28,800 vibrations per hour, versus 21,600 for the 2385. These are published specifications, not independent accuracy or endurance test results.
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| Specification | Calibre 6401 | Calibre 2385 |
|---|---|---|
| Development | Developed entirely in-house over five years, according to AP’s release account published by Europa Star. | Predecessor; Europa Star says it was introduced in 1997. |
| Power reserve | 55 hours, per AP’s release account. | 40 hours, as reported by launch coverage. |
| Frequency | 28,800 vibrations per hour, per Hodinkee. | 21,600 vibrations per hour, per Hodinkee. |
| Caseback on the 38 mm watch | Sapphire display caseback, exposing the movement. | Not a display caseback on the previous 38 mm chronograph, according to the release account. |
Integrated chronograph with column wheel and vertical clutch
Calibre 6401 uses an integrated chronograph architecture, a column wheel and a vertical clutch. The release account says AP simplified and patented the clutch mechanism to reduce the number of components and unnecessary play, and that the pushers therefore require less pressure. Those benefits are manufacturer-reported design claims; the cited coverage does not establish hands-on findings about pusher feel, reliability or durability.
Despite the column wheel and vertical clutch, this calibre is not a flyback. Hodinkee specifically notes the absence of a flyback function. It should not be conflated with Calibre 4401 in the 41 mm Royal Oak Chronograph, which is an integrated flyback movement.
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- Fit for Model Number: 26315ST.OO.1256ST.01; 26320OR.OO.D002CR.01; 26331OR.OO.D315CR.01; 26331ST.OO.1220ST.03; 26331ST.OO.1220ST.01...
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Repositioned counters and date
The counter arrangement has changed: the minute counter is at 9 o’clock and the hour counter at 3. The date remains between 4 and 5 o’clock, but launch coverage describes it as positioned more centrally. AP’s release account also specifies an instant-jump date.
A first display back for the 38 mm chronograph
The sapphire caseback lets owners see Calibre 6401 and its finishing; the release account describes it as a first for a 38 mm Royal Oak Chronograph. Details named there include an openworked monobloc rotor, Côtes de Genève, alternating satin brushing and polished chamfers. The 38 mm case diameter remains unchanged. Fratello Watches reports 11.1 mm thickness and 50 m water resistance for the launch watches; those figures are its launch specifications, not figures cited here from an official AP technical sheet.
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- Compatibility & Size: Watch Band Bracelet, compatible with Audemars Piguet Royal Oak Offshore Safari Stainless/S, Royal Oak Offshore models.
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- Compatibility Check: Double-check your watch's requirements and compatibility details to ensure the product meets your needs. This will help you avoid any issues with returns or exchanges.
- Aftermarket Product: This is an aftermarket/generic made to original factory specs for a precise fit.
Three launch versions of the 38 mm Royal Oak Chronograph
Launch coverage identifies three variants. References below follow the launch reports; AP’s current US pages append “-B” to the steel and standard pink-gold references.
| Launch version | Reference in launch coverage | Case, dial and bezel | Reported launch price |
|---|---|---|---|
| Steel | 26450ST.OO.1356ST.01 | Stainless steel, blue dial, standard bezel. | US$43,000 in Hodinkee’s February 3, 2026 US-market report; €39,200 in Fratello Watches’ February 4, 2026 euro-market report. |
| Pink gold | 26450OR.OO.1356OR.01 | 18-carat pink gold, dark-grey dial, standard bezel. | US$84,500 in Hodinkee’s February 3, 2026 US-market report; €77,000 in Fratello Watches’ February 4, 2026 euro-market report. |
| Pink gold with diamond-set bezel | 26450OR.ZZ.1356OR.01 | 18-carat pink gold, sand-gold-toned dial, diamond-set bezel. | US$91,600 in Hodinkee’s February 3, 2026 US-market report; €83,500 in Fratello Watches’ February 4, 2026 euro-market report. |
These are launch-period prices reported by the named publications in the specified markets, not confirmation of current retail prices, availability or secondary-market value. AP’s official product pages are the appropriate place to check current regional information.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the movement change means for the collection
The headline is a mechanical renewal that also changes how the 38 mm chronograph presents itself: a longer stated reserve, updated counter positions and a view of the movement through the new sapphire back. The release account frames Calibre 6401 as a new chapter for the line; it does not establish independent performance claims such as measured accuracy. For buyers comparing the new versions, the choice among steel with blue, pink gold with dark grey, and diamond-set pink gold with sand gold is the visible distinction, while the new calibre is shared across the launch story.
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