The origins of LMDh trace back to IMSA's search for a next-generation top-class platform after the Daytona Prototype International (DPi) era. In January 2018, IMSA extended DPi homologation periods and began exploring what came to be called DPi 2.0 — an evolution of the LMP2 platform incorporating hybrid technology. Simultaneously, the FIA World Endurance Championship was developing the Le Mans Hypercar concept to replace LMP1. By mid-2019, discussions between IMSA and the ACO turned toward convergence: WEC CEO Gerard Neveu publicly acknowledged efforts to align performance targets between the two platforms so cars from either ruleset could race each other head-to-head.
By November 2019, Toyota, Ford, Porsche, and McLaren had all expressed interest in convergence, though on different grounds. Toyota wanted the arrangement to accommodate hybrid technology; McLaren called LMH costs prohibitive and pushed for DPi integration into WEC. The growing manufacturer consensus set the stage for a formal announcement.
On 24 January 2020, at the Daytona International Speedway ahead of the 24 Hours of Daytona, IMSA and the ACO jointly revealed the LMDh regulations. The announcement confirmed that LMDh cars would be eligible for both the WEC Hypercar class and IMSA's premier prototype class, and that they would race directly against LMH-spec cars under a unified Balance of Performance framework.
The ruleset drew heavily from LMP2 architecture. Draft regulations released in May 2020 specified a standardised 50 kW (67 hp) hybrid system — abandoning earlier plans to allow bespoke manufacturer hybrid units — combined with a maximum total output of 500 kW (670 hp) and a minimum weight of 1,030 kg. The bodywork was to follow a single package, tyres supplied by a single manufacturer, and a global Balance of Performance system would equalise LMDh and LMH machinery.
The hybrid system's mechanical components were divided among established suppliers: Xtrac provided the gearbox with integrated motor-generator unit, Bosch supplied the motor-generator hardware, and Williams Advanced Engineering supplied the battery pack. Four chassis constructors were approved — Dallara, Ligier, Multimatic, and Oreca — each offering a base platform that manufacturers could style with bespoke bodywork, creating visual differentiation while keeping underlying costs controlled.
IMSA confirmed in January 2022 that its new top class would be named GTP, invoking the prestigious Grand Touring Prototype name from 1980s American motorsport. The class debuted at the 2023 24 Hours of Daytona with four manufacturers and nine cars. LMDh machinery dominated IMSA's GTP class throughout 2023 and 2024, as no LMH-spec car had yet been homologated for IMSA competition.
In the WEC, LMDh cars made their series debut in the 2023 season, competing in the Hypercar class alongside Toyota, Glickenhaus, and Peugeot LMH entries, as well as an Alpine LMP1 holdover. The first time an LMH car appeared in an IMSA event came only at the 2025 12 Hours of Sebring, when the Aston Martin Valkyrie AMR-LMH made its IMSA debut.
LMDh attracted a broad manufacturer roster, including Porsche, BMW, Cadillac, Acura, Lamborghini, and Alpine among the early participants. The ruleset's appeal lay in its cost discipline: by mandating common chassis platforms and hybrid components, it reduced the engineering investment compared to bespoke LMH programmes while still delivering factory-level performance and brand differentiation through styling.
The convergence of LMDh and LMH under a shared Balance of Performance marked one of the most significant governance decisions in endurance racing in decades, effectively creating a single global top-class prototype category capable of being contested on two continents under two series banners. As of 2025, plans were in place to extend Hypercar-class LMDh eligibility to the Asian Le Mans Series from the 2026/27 season onward.