This study describes ARV concentrations in the breastmilk and maternal plasma of 21 Swiss mothers on HIV treatment (2019-2021), to estimate daily infant ARV dose from breastfeeding.  Infant plasma ARV concentrations were also measured.  All mothers had viral load < 50 copies/mL (ideally throughout pregnancy) and routine clinical evaluation occurred via monthly visits per Swiss care guidelines.  No infants received post-exposure prophylaxis, as per Swiss recommendations.  Maternal breastmilk and plasma samples were obtained at 1-, 3-, and 6-month follow-up visits after delivery.  Infants were tested at 1 and 6 months of age by PCR and again 3 months after weaning; serologic testing was performed at 18-24 months of age.  Most mothers were receiving INSTI-based treatment (1 bictegravir, 3 dolutegravir, 10 raltegravir), 2 were on rilpivirine-based combinations, and 2 were on ritonavir-boosted darunavir.  Three were receiving tenofovir alafenamide (TAF).  No HIV transmissions were identified.  Sample analyses demonstrated rilpivirine and tenofovir [derived from TAF] transfer well in breastmilk (similar to other NNRTIs and most NRTIs).  By contrast, darunavir/ritonavir (like other PIs) has low transfer.  INSTI transfer was variable: bictegravir and dolutegravir have low transfer, and raltegravir has moderate-high transfer.  Very low or undetectable levels for rilpivirine, raltegravir, darunavir/ritonavir, and tenofovir [derived from TAF] were observed in infants.  Efavirenz, nevirapine, and dolutegravir were detectable in infants.  Overall, the estimated daily infant ARV dose from breastfeeding was low for all evaluated ARVs and fell within the safety threshold (exposure index < 10%).