A. Einstein, "Relativity", Chapter 22:

"A curvature of rays of light can only take place when the velocity of
propagation of light VARIES with position."

So, according to Einstein, an observer positioned in a gravitational
field will measure a VARIABLE, not constant velocity of light. The
observer can measure, for instance, the frequency shift and, if
Einstein is right, a non-zero frequency shift corresponding to the
changing velocity of light will be detected.

Einsteinians never discuss this problem voluntarily but, when pressed,
they produce a combination of words more or less like this: The
velocity of light is constant only locally, non-locally it is variable.
The meaning of this combination of words, especially when applied to
Einstein's assertion, is a grand secret between Einsteinians.

Pentcho Valev