> In my experience, direct coordination on interfaces tends to create unnecessary special cases (hey, can you add this field to your API, just for us?) which add complexity and make maintenance more difficult down the line.

If you just implement all requests directly, you're for sure going to end up with a horrible interface. You should approach API design the same way that UX/PM approaches UI and feature design: take the time to understand _why_ your partner teams/engineers are requesting certain changes and figure out the right interface to address their problems.

Oh absolutely, but direct communication between teams is not the right method for that. Which is why every product, no matter how "micro" a service, needs to have a dedicated product owner/manager who is responsible for defining functional requirements.

Edit: I just noticed that "PM" in parent comment. Basically, product managers are not just for UI and customer-facing products.

The idea that "functional requirements" can be decided independently from "technical architecture", as opposed to in interplay with each other, is exactly the opposite of what I've learned from good experiences with "agility", although some people seem to somehow take it that the opposite.

But yes, you can never just do what "the users" ask for. The best way to understand what they need is to be in conversation with them. Silo'ing everyone up isn't going to make the overall product -- which has to be composed of all these sub-components working well with each other -- any better.

> The idea that "functional requirements" can be decided independently from "technical architecture"

Oh it absolutely can; it's just that it usually is not a good idea. But I'm not talking about the process of reaching that decision, I'm talking about the responsibility to reach them. Functional and technical decisions are separate, but in most cases should be defined in conjunction.

> Silo'ing everyone up isn't going to make the overall product

This is true for certain types of product, and less so for others; you need to clearly understand what type of product you're building, and be ready to adapt as it changes (or you have a better understanding of it). In a nutshell, the more compartmentalised a product is, the isolation between the teams becomes more beneficial. Which brings us full circle back to Conway's Law.

> But I'm not talking about the process of reaching that decision, I'm talking about the responsibility to reach them

Of course you're talking about the process. Your claims that "direct communication between teams is not the right method for that," and "communication between teams working on discreet, separate units can become detrimental," for instance, are about process.

I don't think this conversation is going anywhere, but from my experience, lack of communication between teams working on discrete, separate units (that are expected to be composed to provide business value), can become detrimental. And that's about process.