On 2 July 2015, IMSA announced the base regulations for an unnamed new Prototype class scheduled to debut in 2017. The new formula was intended to replace the third-generation Daytona Prototypes and to absorb the LMP2 class, which would become obsolete as a result of new global LMP2 regulations. The core concept required manufacturers to build their cars on a standard LMP2-derived prototype base while permitting custom bodywork in designated development zones, blending manufacturer identity with cost-controlled engineering.
Restricted areas — where custom bodywork was expressly prohibited — included the rear wing and its mounts, the engine cover fin, the entire underfloor (splitter, floor, and diffuser), and the area directly behind the front tyres. Manufacturers were also barred from shaping the outer regions of the nose, a zone traditionally used for dive planes on prototypes.
On 1 October 2015, IMSA formally confirmed engine and bodywork guidelines and announced the class name: Daytona Prototype International. The homologation period was set at a minimum of four years, from 2017 through 2020, with the stated aim of allowing competitors to maximise their investments.
Production-based engines were mandated for the class. Turbocharged four- and six-cylinder units operated without restrictors, with boost levels governed on an RPM-basis to balance the inherent acceleration advantages of forced induction over naturally aspirated engines, which used sonic air restrictors.
On 11 January 2016, IMSA confirmed that each manufacturer had to commit to a specific combination of engine and bodywork package and would be locked into an alliance with a single chosen chassis manufacturer. This was a significant departure from the preceding Daytona Prototype formula, which had permitted one set of bodywork — such as the Corvette DP shell — to be used across different chassis platforms. Factory teams were permitted, and manufacturers faced no obligation to sell chassis to customer teams. IMSA implemented a Balance of Performance process to maintain competitive parity between DPi and LMP2-specification cars.
On 24 January 2018, IMSA extended the homologation periods for DPi, LMP2, and GTE-class machinery by one additional year, citing the FIA World Endurance Championship's transition to a winter calendar as the cause; the shift delayed homologation cycles globally by approximately six months. DPi cars, originally confirmed through 2020, thereby became eligible through at least the end of the 2021 season. In 2020, eligibility was extended further to the end of 2022 — a consequence of the COVID-19 pandemic and the delayed readiness of LMDh machinery for the 2022 season.
An early plan called for DPi cars to race at the 24 Hours of Le Mans within the LMP2 category, fitted with standard LMP2 bodywork and regulated via a spec Cosworth ECU. However, subsequent IMSA regulation changes removed the spec ECU and other mandated data logging systems from the DPi platform. ACO President Pierre Fillon publicly voiced his displeasure with these changes, and the divergence ultimately rendered DPi cars ineligible to compete at Le Mans in LMP2. Discussions shifted to the LMP1 Privateer class, but these too did not produce a workable pathway, leaving DPi cars absent from La Sarthe throughout the class's existence.
The DPi formula was replaced from the 2023 season by the LMDh class — a jointly developed IMSA-ACO category. Unlike DPi, LMDh cars are cross-eligible for the 24 Hours of Le Mans and the FIA World Endurance Championship, resolving the trans-Atlantic incompatibility that had prevented DPi from reaching Le Mans.
The DPi era produced competitive manufacturer battles between Acura, Cadillac, Mazda, and Nissan across six seasons of WeatherTech SportsCar Championship racing. The class demonstrated that a formula combining LMP2 underpinnings with manufacturer-specific bodywork and production-based powerplants could sustain a viable top-tier prototype class for North American endurance racing, and it directly informed the multi-platform thinking that produced the LMDh framework which followed it.
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