If it's not, we can still rely on the parents field to compute it.
It seems to be working fine at first glance:
$ # in bash
$ echo $SHLVL
1
$ zsh
$ echo $SHLVL
2...though SHLVL is defined in the Bash man page as follow:
SHLVL Incremented by one each time an instance of bash is started.
Maybe it's also used the same way by Zsh.
pawamoy / shell-history
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