  We present an efficient implementation of the equation of motion oscillator
strengths for the closed-shell multilevel coupled cluster singles and doubles
with perturbative triples method (MLCC3) in the electronic structure program
eT. The orbital space is split into an active part treated with CC3 and an
inactive part computed at the coupled cluster singles and doubles (CCSD) level
of theory. Asymptotically, the CC3 contribution scales as $O(n_\text{V}
n^3_\text{v} n^3_\text{o})$ floating-point operations (FLOP), where $n_V$ is
the total number of virtual orbitals while $n_\text{v}$ and $n_\text{o}$ are
the number of active virtual and occupied orbitals, respectively. The CC3
contribution, thus, only scales linearly with the full system size and can
become negligible compared to the cost of CCSD. We demonstrate the capabilities
of our implementation by calculating the UV-VIS spectrum of azobenzene and a
core excited state of betaine 30 with more than 1000 molecular orbitals.
