A gas knife system for an additive manufacturing system can include one or more gas delivery members configured to move relative to a build area of the additive manufacturing system, and an inlet conduit configured to supply gas to the one or more gas delivery members while the one or more gas delivery members are moved relative to the build area. The system can also include one or more gas collection members configured to move relative to the build area of the additive manufacturing system, and an outlet conduit configured collect gas from the one or more gas collection members while the one or more gas collection members move relative to the build area.