Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the efficacy of the additive consisting of Companilactobacillus farciminis (formerly Lactobacillus farciminis) CNCM I‐3740 (tradename: Biacton®) for chickens for fattening, turkeys for fattening and laying hens. The additive is a preparation containing viable cells of C. farciminis CNCM I‐3740 at the minimum concentration of 1 × 109 CFU/g additive. It is intended to be used as a zootechnical additive in feed for chickens for fattening, turkeys for fattening and laying hens at the recommended application level of 5 × 108 CFU/kg complete feed. In the context of previous opinions, no conclusions could be drawn on the efficacy of the additive in any of the target species based on the data provided. As regards chickens for fattening, in the former opinions the supplementation of the additive at the recommended level showed a significantly greater weight or weight gain compared to birds in the control group only in two studies. New statistical analysis data of one efficacy trial were submitted. The results showed that Biacton® supplemented at 8.5 × 108 CFU/kg feed or at higher levels significantly improved the feed to gain ratio of chickens for fattening compared to control birds or to birds receiving the additive at the recommended level. Therefore, the Panel concluded that Biacton® has the potential to be efficacious in chickens for fattening at the concentration of 8.5 × 108 CFU/kg complete feed. This conclusion was extrapolated to turkeys for fattening.