The maximum distance that QSFP28 (Quad Small Form-factor Pluggable 28) transceivers can reach depends on the specific type and technology of the transceiver, as well as the optical fiber used. QSFP28 transceivers are commonly used for high-speed data communication in data centers and telecommunications networks.

As of my last knowledge update in January 2022, the typical distance ranges for QSFP28 transceivers are as follows:

SR4 (Short Range 4): This type is designed for short-range connections within a data center. It typically supports distances up to 100 meters over multimode fiber.

LR4 (Long Range 4): LR4 transceivers are designed for longer distances. They can support up to 10 kilometers over single-mode fiber.

ER4 (Extended Range 4): ER4 transceivers are designed for extended distances. They can support up to 40 kilometers over single-mode fiber.

ZR4 (Zero Dispersion Range 4): ZR4 transceivers are optimized for even longer distances. They can support up to 80 kilometers over single-mode fiber.

It's important to note that these are general distance ranges, and actual performance may vary based on factors such as the quality of the optical fiber, the specific transceiver model, and environmental conditions. Additionally, newer developments and technologies may have been introduced since my last update, so it's advisable to refer to the latest specifications and documentation provided by the transceiver manufacturer for the most accurate and up-to-date information.