FELIX is a readout system based on a custom-designed PCIe card developed for the ATLAS experiment at the LHC. The FELIX card, hosted by a commodity server, allows to interface optical links from custom radiation-tolerant front-end electronics to a commodity switched Ethernet network. The project was launched in 2014 as part of the ATLAS upgrade for the 2022-2026 data-taking period. The FELIX system is currently in production, and a new iteration is being developed for the next ATLAS upgrade. From 2030 until the end of the experiment lifetime, the FELIX system will read out all components of the ATLAS detector handling a total throughput of 5 TB/s at a 1 MHz data rate.