  Our position inside the Galactic disc had prevented us from establishing an
accurate rotation curve, until the advent of Gaia, whose third data release
(Gaia DR3) made it possible to specify it up to twice the optical radius. We
aim to establish a new rotation curve of the Galaxy from the Gaia DR3, by
drastically reducing uncertainties and systematics, and with the goal to
provide a new estimate of the mass of the Galaxy. We have compared different
estimates, established a robust assessment of the systematic uncertainties, and
addressed differences in methodologies, particularly regarding distance
estimates. This results in a sharply decreasing rotation curve for the Milky
Way, the decrease in velocity between 19.5 and 26.5 kpc is approximately 30 km
s$^{-1}$. We have identified, for the first time, a Keplerian decline of the
rotation curve, starting at $\sim$ 19 kpc and up to $\sim$ 26.5 kpc from the
Galaxy center, while a flat rotation curve is rejected with a significance of
3$\sigma$. The total mass is revised downwards to $2.06^{+0.24}_{-0.13}\times
10^{11}\ M_{\odot}$, in agreement with an absence of significant mass increase
at radii larger than 19 kpc. The upper limit of the total mass was evaluated by
considering the upper values of velocity measurements, which leads to a strict,
unsurpassable, limit of $5.4\times 10^{11}\ M_{\odot}$.
