Rare decays and searches for exotic signatures at LHCb: purely leptonic decays

A review of the experimental status of purely leptonic ${B^0_{[s]}\to\ell^+\ell^-}$ decays is given and the new analysis of ${B^0_{[s]}\to\mu^+\mu^-}$ observables with the LHCb experiment is presented. The new results are the most precise single experiment measurements of the quantities to date and are consistent with the Standard Model. However, they also match the recent anomalies found in $b\to s\ell\ell$ transitions excellently.