The TerraMaster F4-425 Pro is a high-end Network Attached Storage (NAS) device designed for users who need large amounts of storage and advanced computing power. It offers four bays for 2.5 or 3.5-inch hard drives and three M.2 NVMe PCIe 3.0 slots, allowing for up to 152 terabytes of storage capacity. The device is powered by an Intel Core 3 N350 processor and comes with 16 gigabytes of DDR5 RAM. It features the same connectivity options as the F4-425 Plus model, including two 5 GbE network ports, three USB A ports, a USB C port, and an HDMI output. It is the first TerraMaster model to ship with version 7 of the TOS operating system, which includes a local "AI" layer for enhanced features. It competes with other high-end NAS devices like the Ugreen NASync DXP4800 GT and the Synology DS925+. Retailers list the F4-425 Pro at around 600 euros without hard drives. The F4-425 Pro has a sleek, compact design with an aluminum casing that allows easy access to internal components by removing four screws. It includes four sliding compartments for hard drives, each labeled with a number and a status LED for monitoring. The lack of a locking mechanism for the drive bays might be a drawback in professional settings where security is a priority. Connectivity ports include a front USB A port, two USB A ports that support 10 Gbps transfer speeds, a USB C port with the same speed, two 5 GbE network ports, and an HDMI port. The HDMI port is mainly used for maintenance or installing an alternative operating system. The device uses a single 120 mm fan located at the back of the chassis for cooling. At rest, the temperature of the hard drives is about 5 degrees Celsius above the ambient room temperature, while NVMe solid-state drives can reach over 50 degrees Celsius without additional cooling. The fan operates quietly, even under load. Performance testing shows the Intel Core 3 N350 processor provides strong performance, placing the F4-425 Pro near the top in most benchmarks. The integrated graphics support decoding of H.264, H.265, MPEG-4, and VC-1 video formats up to 4K resolution at 60 frames per second. It can transcode up to four 4K videos to 1080p resolution simultaneously in optimal conditions and supports hardware decoding of VP9 and AV1 codecs. Storage performance varies depending on the type of drive and the interface used, with specific read and write speeds measured during testing. The F4-425 Pro comes with TOS 7, a major update to TerraMaster’s operating system that improves performance and user experience. The file manager has been redesigned to offer more features, resembling a full desktop computer. TOS draws design inspiration from Synology’s DSM and Ugreen’s UGOS, but it offers a more user-friendly interface than Synology, though it is still less refined. The operating system allows for customization through apt, a package management system, and enables users to install alternative operating systems via the HDMI port. AI features are integrated through the OpenClaw orchestrator, which requires an external large language model (LLM), such as ChatGPT, Claude, or Gemini, to function—adding an extra cost. While the AI features are functional, they are complex to set up and rely on external services, making them less accessible to non-expert users. The TerraMaster F4-425 Pro is available at a recommended retail price of 839 euros.