[colinmcd]

Ecosystem libraries would need to switch from a single peer dependency on Zod to two optional peer dependencies. Despite "optional peer dependencies" technicall being a thing, its functionally impossible for a library to determine which of the two packages your user is actually bringing to the table.

Let's say a library is trying to implement an `acceptSchema` function that can accepts `Zod3Type | Zod4Type`. For starters: those two interfaces won't both be available if Zod 3 and Zod 4 are in separate packages. So that's already a non-starter. And differentiating them at runtime requires knowing which package is installed, which is impossible in the general case (mostly because frontend bundlers generally have no affordance for optional peer dependencies).

I describe this in more detail here: https://x.com/colinhacks/status/1922101292849410256

[ts17631]

Thanks a lot for zod and really looking forward to trying out the new version! Also as a primary Go developer this issue just has been really interesting to read about. Go avoids this issue by just not having peer dependencies and relying on the compiler to not bundle unused code - or just live with huge binaries when it doesn't work out :-)

I am still curious about the `zod4` idea though. Any thoughts on adding an `__api_version` type of property to distinguish on to all of zod's public types? Perhaps it's prohibitive code-size wise but wondering if it's possible somehow. Then downstream libraries could differentiate by doing the property check.

Just wanted to share the idea but the current state seems ok too.