  The $^{238}$U to $^{235}$U fission cross section ratio has been determined at
n_TOF up to $\sim$1 GeV, with two different detection systems, in different
geometrical configurations. A total of four datasets have been collected and
compared. They are all consistent to each other within the relative systematic
uncertainty of 3-4%. The data collected at n_TOF have been suitably combined to
yield a unique fission cross section ratio as a function of the neutron energy.
The result confirms current evaluations up to 200 MeV. A good agreement is also
observed with theoretical calculations based on the INCL++/Gemini++ combination
up to the highest measured energy. The n_TOF results may help solving a
long-standing discrepancy between the two most important experimental dataset
available so far above 20 MeV, while extending the neutron energy range for the
first time up to $\sim$1 GeV.
