Observable Primordial Gravitational Waves from Cosmic Inflation

I will review briefly how inflation is expected to generate a stochastic background of primordial gravitational waves (GWs). Then, I will discuss how such GWs can be enhanced by a stiff period following inflation, enough to be observable. I will present examples of this in the context of hybrid inflation with $\alpha$-attractors, or a period of hyperkination in Palatini gravity.