Physics
How fast do gravitational waves travel?
Gravitational waves travel at the speed of light. In 2017 a neutron-star merger was seen in both gravity and light, and the two signals arrived within 2 seconds of each other after 130 million years.
Source: Abbott et al. (2017), Astrophysical Journal Letters (GW170817).
Context
At the speed of light, as closely as anyone has been able to measure. In 2017 the merger of two neutron stars, GW170817, was detected in gravitational waves and then seen in light.
The two signals arrived within about 2 seconds of each other after travelling for 130 million years. That rules out any meaningful speed difference between gravity and light.
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