  The Hubble diagram (HD) of Gamma-Ray Bursts (GRBs) having properly estimated
redshifts is compared with the predicted one for the Chaplygin gas (CG), a dark
energy candidate. The CG cosmology and that of Friedmann and $\Lambda$-CDM
models are studied and confronted to the GRBs observations. The model-to-sample
$\chi^2$ statistical analysis indicates the CG model as the best fit. The
present GRBs HD plot exhibits a marked trend: as one goes back in time, it gets
much closer to the predict HD for a Friedmann universe. This clear trend
conclusively demonstrates that a transition from decelerate to accelerate
expansion did take place. However, contrarily to claims based on supernovae
type Ia, the transition redshift lies somewhere between $\sim 2.5 < z \simeq
3.5$ rather than at $z \sim 0.5-1$. All of these striking features of the GRBs
HD constitute the most robust demonstration that the Chaplygin gas can in fact
be the universe's driving dark energy field.
