Output only. The model's estimate of the probability that
its answer is correct and grounded in the input passages.
A low answerable_probability indicates that the answer might
not be grounded in the sources.
When answerable_probability is low, some clients may
Display a message to the effect of "We couldn’t answer
that question" to the user.
Fall back to a general-purpose LLM that answers the
question from world knowledge. The threshold and nature
of such fallbacks will depend on individual clients’ use
cases. 0.5 is a good starting threshold.