Involved in ciliogenesis (By similarity). It is required for appropriate acetylation and polyglutamylation of ciliary microtubules, and regulation of cilium length (By similarity). Acts as a positive regulator of hedgehog (Hh) signaling (PubMed:29459677). May participate in the trafficking and/or retention of GLI2 and GLI3 proteins at the ciliary tip (PubMed:29459677). Interacts with TOGARAM1, CCDC66, CEP104, CSPP1 and CEP290. Localized to the proximal region in cilia. Stimulation of Hh signaling leads to redistribution of ARMC9 toward the ciliary tip within 6 hours, follow by a gradual return to its original proximal location (PubMed:29459677). Localizes to the daughter centriole of the primary cilium in RPE1 cells (By similarity).