Thanks for pointing out Arazzo—I wasn't previously aware of it, so I appreciate the reference and will definitely take a closer look.

That said, based on an initial read, it seems like Arazzo and links are solving different problems. Arazzo provides a client-side flow—essentially a "how-to" guide for achieving a particular outcome. Links, on the other hand, describe what is possible at a given point from the server’s perspective—more like a snapshot of server state transitions following an operation.

If I were to use an analogy: Arazzo is like directions, optimized for getting to a destination efficiently. Links are more like signposts—useful for freeform exploration and understanding what actions make sense at each state.

I think a key question here is whether links are considered deprecated or being phased out in favor of Arazzo. If that's the direction the spec is going, I won’t try to push back too hard—clearly a lot of thought has gone into that shift. But if links are still seen as a valid, maintained concept, then I believe adding expected responses fits well within their role and improves their utility.

In short, to me these features serve complementary use cases, not competing ones.

@elmanm thanks, this is a good analysis and helpful in terms of thinking about use cases.

The Link Object is not being deprecated at this time, but we are trying to better understand what makes sense there vs Arazzo vs HTTP Link headers (see #4740 for improved support proposed to go into 3.2). Some of this is me personally trying to get a good sense for this — other folks may have a better idea of where we're going in this area. Link Objects also have capabiliities that HTTP Link headers lack, so really we have three ways of describing how to connect operations that each have somewhat different capabilities.

Since we're in the final phases of 3.2, there's plenty of time to have this discussion open. You might also want to look at into some Moonwalk discussions (Moonwalk started as a project to come up with 4.0 but is becomiing more of an idea lab for 3.x as incremental stess to 4.0): OAI/sig-moonwalk#58 is a proposal for links from @mikekistler while OAI/sig-moonwalk#30 is a more general discussion about resources vs operations.