The U.S. party may simply have visited Russia to see an example of Avangard, or even just its warhead, which is an unpowered hypersonic boost-glide vehicle, and get briefed on how the Kremlin sees the weapon as fitting into the terms of New START. The treaty, which the two countries signed in 2009, puts hard limits on total numbers of how many intercontinental ballistic missiles (IBCM), submarine-launched ballistic missiles (SLBM), and heavy bombers each country can have deployed at any one time.

There are also limitations on how many "warheads" and deployed and non-deployed "launchers" the two countries can possess. These terms are defined somewhat confusing, with each individual reentry vehicle inside an ICBM or SLBM and every nuclear-capable heavy bombers counting as "warheads." Bombers, along with missile silos and individual launch tubes on ballistic missile submarines, qualify as "launchers" under the agreement.

There had been some question in the past about whether Russia would even agree that Avangard was covered under New START. In January 2019, the Russian government had sent a letter to members of Congress, which subsequently leaked out into the open press, that specifically stated that "weapons being developed by Russia that do not use ballistic trajectories of flight moving to a target ... have nothing to do with the strategic offensive arms categories covered by the Treaty."

Avangard uses a UR-100N UTTKh ICBM as the rocket booster to loft the hypersonic boost-glide vehicle to the appropriate altitude and boost it to the required speed. Afterward, the independently maneuverable weapon then travels along a flatter, distinctly non-ballistic trajectory toward its target. This is one of the core benefits that hypersonic weapons offer over traditional ICBMs, which have more predictable flight paths and signatures after launch. This makes them harder to spot, track, and potentially engage with missile defense systems. This also gives an opponent less advance warning and, as a result, fewer opportunities to relocate critical assets or otherwise respond to an incoming strike.