With two days to go until the 130th Boston Marathon, attention inside the super-shoe community has pivoted from this spring's visible launches — the Adidas Adios Pro Evo 2, the Hoka Cielo X1 3.0 and the Asics Superblast 3 — to the rumoured shoe that has not yet been named. Multiple sources close to Nike's Boston presence this week have told the running press that the brand is preparing to let selected Bank of America professional-field athletes race on what the company internally refers to as "Dev 164," a prototype that industry trackers have been calling the Alphafly 4 since winter. Nike has neither confirmed nor denied any Monday debut, but several of the clues around Boston this weekend point in that direction.
The first is the timing of Nike's latest Alphafly 3 colourway. On Thursday 16 April, the brand dropped the "White/Volt" Alphafly 3 through Nike.com and select third-party retailers, a colour story that the running-shoe release sites had pegged as a final refresh for the model before the generation-four transition. Nike has historically paired a terminal "volt" colourway with the imminent arrival of a successor platform — the Vaporfly 3 rolled over to the Vaporfly 4 along a similar timeline in 2025 — and the pattern now appears to be repeating. The parallel Kipchoge-branded "No Human Is Limited" Alphafly 3, still heavily featured on the Newbury Street storefront, would likely be the last civilian Alphafly 3 story of the season.
The second is the shoe itself. Industry photographers have tracked "Dev 164" since the 2025 Chicago Marathon, where Jacob Kiplimo raced to a 2:02:23 Ugandan record in a blacked-out prototype that Nike later confirmed had been submitted to and cleared by World Athletics. Reports since have pointed to an upper configuration closer to the Vaporfly 4, a reworked carbon plate with more flex under the forefoot, a taller stack of Nike's proprietary ZoomX foam, and a revised Air Zoom pod cluster positioned more deeply in the midsole than on the Alphafly 3. If those design choices hold, the shoe would push against the 40mm World Athletics stack-height limit while trying to preserve the distinct propulsion signature that has defined the Alphafly platform since 2020.
What remains unclear is how visible any debut would be. Nike has grown cautious about publicly showcasing unreleased road shoes on race day after the blowback around the Vaporfly prototype in 2019 and the more recent discourse over its development-shoe dispensations at the last two Tokyo Marathons. Some sources suggest the Boston debut may be limited to one or two elite men or women racing in a lightly obscured colourway rather than a full branded rollout; others expect a low-key press-kit confirmation to run alongside the Monday finish-line broadcast on WBZ and ESPN+. Either path would put the Alphafly 4 on the road roughly a year before consumer availability, keeping with Nike's pattern of racing a platform for one full spring season before retail.
For the elite field itself, the strategic calculation is familiar. The Alphafly 3 still holds the men's marathon world record thanks to the late Kelvin Kiptum's 2:00:35 in Chicago in 2023, and several of Monday's favourites — notably defending champion John Korir, Benson Kipruto and American hope Conner Mantz's replacements — are Nike contracted athletes who have lived with the Alphafly 3 for two full racing cycles. Switching to a new platform during one's peak event is a non-trivial risk, particularly on a downhill opener like Boston's. Whether any of them chooses to make that leap on Monday — or whether Nike instead lets the Alphafly 4 narrative bake until the London or Berlin cycle — will shape the super-shoe conversation for the rest of the year.