DC's "Rebirth" ongoing Superwoman will 'conclude' with issue #18, according to a solicitation for the third collected volume published in the Edelweiss catalogue. Here's how it reads:
The conclusion to the adventures of DC’s newest hero in SUPERWOMAN VOL. 3, as a part of DC Rebirth!
Searching for an explanation of the source of her powers, Lana traces her steps back to high school with a teenage Clark Kent in Smallville. With Lana’s role as Superwoman hanging in the balance, Lex Luthor makes an unexpected appearance.
From writer K. Perkins (SUPERGIRL) comes the finale of one of the most unique tales in DC history with SUPERWOMAN VOL. 3! Collects SUPERWOMAN #13-18.
Single issues of the series are solicited through October 2017's Superwoman #15, so if accurate the series “finale” (#18) would arrive in January 2018.
Superwoman Vol. 3 is scheduled for release May 29, 2018.