arcstat has been integrated into illumos as of 1186:
<a href="https://github.com/illumos/illumos-gate/commit/d0054224e0ba320a05d1c27de508dc5224ff99d1">link</a>.

I'm leaving this repo here for historical reference.
From now on, please treat the 
[illumos version](https://github.com/illumos/illumos-gate/blob/master/usr/src/cmd/stat/arcstat/arcstat.pl) 
as canonical.

You can view the manpage for arcstat(1M) [here](https://smartos.org/man/1m/arcstat).