As the title says, if I use Street Informants, can my opponent pass to end the action phase?

Why would it? Something has happened. You've exhausted a support to trigger an effect, looking at your opponents hand.

From my understanding, it should only a pass if you essentially pay a cost for zero effect, e.g. exhausting Backup Muscle with no damage to move.

Fair enough, I saw this question in another thread with no answer, questioning if the lack of game state change meant it acted as a pass. I guess knowledge of the opponents hand counts as game state change?

We have no idea, since they've yet to define 'game state.'

Pretty sure if your opponent has cards in hand it's an action. However if your opponent has no cards in hand, it's a pass.

36 minutes ago, Mep said:

Pretty sure if your opponent has cards in hand it's an action. However if your opponent has no cards in hand, it's a pass.

Let's say you have two copies of Street Informants out, and your opponent does have cards in hand. You use one, your opponent takes any action that doesn't alter the makeup of their hand, and then you use the other one. Is the second use an action or a pass?

I think we can safely agree that they'll rule that using Street Informants won't count as a pass.

The more interesting question, IMHO, is whether they'll actually fix that very awful rule with the SoR update, or if they'll just make something up.