Hugo will default to opening all links in the current tab. I wanted to modify it so that links to other websites open in a new tab, but links to other pages on my blog open on the current tab.

Hugo has some documentation (this will open in a new tab :)) that served as a starting point.

Put this snippet in your blog’s layout/_default/_markup/render-link.html file

{{- $u := urls.Parse .Destination -}}
<a href="{{ .Destination | safeURL }}"
   {{- with .Title }} title="{{ . }}"{{ end -}}
   {{- if $u.IsAbs }} rel="external" target="_blank"{{ end -}}
>
    {{- with .Text }}{{ . }}{{ end -}}
</a>
{{- /* chomp trailing newline */ -}}

The target="_blank" is the piece that causes the link to open in a new tab.