In an Expression Set, what is required for the output of a Calculation Step to...

In Expression Sets, for any intermediate step (like Calculation) to be referenced in subsequent steps, such as Aggregation, the value must be made available via Output.

B. It must be included in the output – Correct. Each step has an "Include in Output" checkbox. If not checked, its result is not accessible to following steps like Aggregation or Sub Expression.

Incorrect Options:

A. Constants are global but do not affect step dependency.

C. It does not have to be a Calculation Step; any previous step’s output can be used if exposed.

Salesforce OmniStudio → Expression Sets - Step Configuration