Quick DDD terminology question: Say Context B depends on A (e.g. because B uses one of A’s services). Is A always “upstream”, or does this change depending on whether one applies “Conformist” or “Customer/Supplier”?

My 2ç: Conformist is always downstream from the service it conforms to, by definition. In customer/supplier, supplier is upstream, customer downstream, otherwise you'd call it partnership. So no, doesn't change.

That would be my take as well: Conformist and Customer/Supplier are organizational ways to deal with a technical dependency. It would be interesting to see whether @ericevans0 and @VaughnVernon agree.

Officially a Conformist is considered downstream, but why couldn't one or the other or both teams in a Partnership conform? (Not a suggestion.) I view Conformist to means the conforming team accepts the other model as is, not attempting to translate. It's the opposite of ACL.

Customer-Supplier means the Customer stands a chance of getting needed features but there may but angst. (eg Customer is not always right, or Supplier is a hot mess.)

Eric seems to situate Customer-Supplier as teams assigned responsibilities in different contexts of the same system. What if you are in Customer-Supplier with and external decency (subscribed to a model that almost fits your needs)?

Rather than making strict rules about U/D, etc., I think it's best to recognize the impact of being in any dependency and then name those as explicit situations and how those will impact either or both teams. Most times U/D will be clear, but may occur unexpectedly.