I believe they are migrating to a new domain, not sure if this helps but this is the new domain https://pkg.go.dev/golang.org/x/sys

Thank for your apply, michaelolson.

I see golang.org is migrating to the new domain, but the official promised that the migration should not affect dependent downloads. And the reason why I open this issue is that I want to use a third-party libraries, which imports golang.org/x/sys/unix package.

When I executed the go get ${third_party}, I got golang.org/x/sys/unix: unrecognized import path "golang.org/x/sys": reading https://golang.org/x/sys?go-get=1: 404 Not Found error. So I couldn't get this third-party dependency now.

And I think this is a big problem if open-source library which import the golang.org/x/sys/xxx package cannot download.

It may because of the IP detection in the China region, since the go-imports tag is still in the HTML response (https://golang.org/x/sys):

<meta name="go-import" content="golang.org/x/sys git https://go.googlesource.com/sys">

Are you using a VPN?

I am not using VPN.

I agree this problem may because of the IP detection.The HTML response of the url https://golang.org/x/sys is this for me.

<a href="https://golang.google.cn/x/sys">Found</a>.

And the HTML response of this url golang.google.cn/x/sys is not contain the go-imports tag. So I got the reading https://golang.org/x/sys?go-get=1: 404 Not Found error.

cc @dmitshur @rsc

CL 344289 will fix the problem due to redirection.

Now it looks working fine, I can find the go-import metadata in golang.org/x.

Thanks a lot.

Thanks for verifying. Closing as fixed (see related issue #47808 which has more details).
(Thanks for fixing @rsc!)