The path to LMDh began in January 2018 when IMSA announced an extension of homologation periods for LMP2, DPi, and GTE machinery in the WeatherTech SportsCar Championship. Despite calls from manufacturers to retain the DPi platform beyond 2021, then-IMSA President Scott Atherton signalled the organisation was exploring next-generation options.
On 6 May 2019, IMSA announced that the next-generation DPi ruleset — dubbed DPi 2.0 — would evolve from the existing LMP2 platform and incorporate hybrid technology from a single supplier. IMSA VP of Competition Simon Hodgson indicated the regulations would also open more bodywork areas to manufacturer styling, potentially mandating a minimum level of styling from each entrant. By June 2019, discussions with manufacturers had produced no consensus on the voltage level for the hybrid system, though a 400-volt system providing 70–90 kW (90–120 hp) of electric power had emerged as a leading candidate, and it was agreed manufacturers could develop their own hybrid systems.
Following the 2019 "Super Sebring" weekend, WEC CEO Gerard Neveu raised the possibility of integrating DPi into the Hypercar class, subject to performance parity between the platforms. On 31 July 2019, Neveu confirmed an active effort between the ACO and IMSA technical departments to align performance targets, enabling eventual cross-entry competition.
Toyota, the sole LMP1 manufacturer in the WEC, expressed openness to DPi integration on 11 November 2019, provided it did not compromise the display of its hybrid technology. McLaren, after reviewing the LMH technical regulations, declined to pursue an LMH programme, with Racing CEO Zak Brown calling the platform cost-prohibitive and publicly advocating for DPi inclusion in the WEC. Ford and Porsche voiced similar positions. On 15 January 2020, Toyota Racing Development president and general manager David Wilson endorsed convergence, noting it would also provide a compelling reason for Lexus to enter DPi.
On 24 January 2020, at a joint ACO-IMSA press conference held at Daytona International Speedway ahead of the 2020 24 Hours of Daytona, Le Mans Daytona h was formally announced. The regulations were designed to supersede DPi as the top IMSA class and to converge with the incoming LMH rules, allowing both LMH and LMDh cars to compete together in both the WEC Hypercar class and IMSA's premier series.
The original plan had manufacturers building their own hybrid systems, but the draft regulations published in May 2020 abandoned that approach in favour of a standardised 50 kW (67 hp) system. Key specifications included a minimum car weight of 1,030 kg (2,270 lb), a peak combined power output of 500 kW (670 hp), a single bodywork package, a single tyre supplier, and a global Balance of Performance system to equalise LMDh and LMH machinery. The gearbox hybrid system is supplied by Xtrac, with an integrated motor generator unit from Bosch and batteries from Williams Advanced Engineering. Approved chassis suppliers are Dallara, Ligier, Multimatic, and Oreca. In January 2022, IMSA confirmed the class name would be GTP, reviving the designation used in the 1980s.
LMDh cars made their IMSA debut at the 2023 24 Hours of Daytona, with four manufacturers fielding a total of nine cars. LMDh entries constituted the entirety of the GTP class in both 2023 and 2024; the class was joined by an LMH car for the first time when the Aston Martin Valkyrie AMR-LMH entered the 12 Hours of Sebring in 2025.
In the WEC, the Hypercar class launched in 2021 with LMH cars from Toyota, Glickenhaus, and later Peugeot, alongside an Oreca-built LMP1 operated by Alpine. LMDh cars did not compete in the series until 2023. In 2025, it was announced that the Hypercar class would also be permitted to participate in the Asian Le Mans Series with customer teams and Pro/Am driver lineups, making LMDh vehicles eligible for the AsLMS starting from the 2026/27 season.