Background: Many out-of-care people living with HIV have unmet basic needs and are served by loosely connected agencies. Prior research suggests that increasing agencies' coordination may lead to higher quality and better coordinated care. This study examines four U.S. interagency networks in AIDS United's HIV linkage and retention in care program. This study explores changes in the networks of implementing agencies. Methods: Each network included a lead agency and collaborators. One administrator and service provider per agency completed an online survey about collaboration prior to and during Positive Charge. We measured how many organizations were connected to one another through density, or the proportion of reported connections out of all possible connections between organizations. Network centralization was measured to investigate whether this network connectivity was due to one or more highly connected organizations or not. To compare collaboration by type, density and centralization were calculated for any collaboration and specific collaboration types: technical assistance, shared resources, information exchange, and boosting access. To characterize the frequency of collaboration, we examined how often organizations interacted by "monthly or greater" versus "less than monthly." Results: Density increased in all networks. Density was highest for information exchange and referring clients. When results were restricted to "monthly or greater," the densities of all networks were lower. Conclusions. This study suggests that a targeted linkage to care initiative may increase some collaboration types among organizations serving people living with HIV. It also provides insights to policy makers about how such networks may evolve.