\documentclass{article}

\usepackage[version=3]{acro}

\RenewAcroCommand\ac{mo}{\UseAcroTemplate{first}{#1}\IfNoValueF{#2}{#2}}

\DeclareAcronym{uc}{
  short = UC ,
  long = Universal Composability ,
  cite = xxx
}

\begin{document}

We use the \ac{uc}[ model] for\dots

\end{document}
