OK, so here's what I can see from the repo:

Current state: The repo is on v2 (the README says "This is version 2 of Quamina"), the latest release on GitHub is v2.0.0 (Jan 21, 2026), and all the source files are in the root directory — no /v2 subdirectory. The package quamina declarations across the .go files all use package quamina with no /v2 in the imports.

The problem is exactly what Marius described. The go.mod almost certainly still says:

module quamina.net/go/quamina

when it needs to say:

module quamina.net/go/quamina/v2

And that's why go get quamina.net/go/quamina@v2.0.1 spits out:

invalid version: module contains a go.mod file, so module path must match major version ("quamina.net/go/quamina/v2")

Here's the PR you'd want to put together (if you want to help Tim fix this):

1. go.mod — change the module line to module quamina.net/go/quamina/v2

2. All internal imports — grep for "quamina.net/go/quamina" across the codebase and change them to "quamina.net/go/quamina/v2". Looking at the repo, this is actually a library with no internal sub-packages (everything is package quamina in the root), so there may be zero internal import paths to fix. That makes this way easier than most v2 migrations.

3. Vanity domain — the <meta name="go-import"> tag at quamina.net/go/quamina/v2 needs to resolve correctly. Since it's a vanity domain, Tim (or Lauren, who set it up) needs to make sure the redirect works for the /v2 path too. Often this just works if the meta tag uses a prefix match, but it's worth verifying.

4. Tag a new release — after merging, tag v2.0.2 (or v2.1.0 or whatever) and create a GitHub release. The Go module proxy will then pick it up.

5. Optionally — hit https://proxy.golang.org/quamina.net/go/quamina/v2/@v/v2.0.2.info to warm the proxy cache, or just go get it.

The good news is that since this is a single-package library with no sub-packages, it's basically a two-line change (go.mod + maybe updating a go report card badge URL) plus the vanity domain check. Way less painful than most v2 migrations.