CI Cyg is an eclipsing ZAND type star, with a P_orb of 852.9d.  Eclipses are total, and last ~60-70 days. The outburst of 2008 was the first recorded since March 1975.

Analysis of 1,800 observations shown in the above light curve (1979-2020) using the ANOVA method in Peranso, reveal a period of 850.46d +/- 10d, which is in good agreement with the period given in VSX of 852.98d