Japanese Patent Application, JP 2023-137876A was published on September 29, 2023 by Canon Inc. It claims to provide high impact resistance for Canon lenses without sacrificing the lens accuracy.
This is achieved by deforming the lens barrel using a caulking claw. The lens barrel is able to deform as it is built from a plastic resin (see Figure 1).
Historically, EF L series glass is known for its metal and glass construction. These lenses are built tough and are heavy. Recent RF lenses are lighter, but have a more plastic feel to them. The reduced weight and plastic feel has allowed Canon to improve impact resistance, while also reducing weight without impacting accuracy.
While the patent was published on September 29, 2023, it was first filed on March 28, 2022 so its likely we could have already seen this in recent lenses like the 100-300mm f/2.8, though I'm not about to take one of these lenses apart to validate. The good news is that new L series high end glass with plastic contraction should not be viewed as Canon cheating out, but improving shock resistance.
JP 2023-137876A Blueprints