Recommendation ITU-T G.709.6 specifies 400G, 800G, 1.2T and 1.6T FlexO Beyond 400G (B400G) and Beyond 1T (B1T) long-reach interfaces. The Recommendation specifies the structure using forward error correction (FEC) codes with a higher coding gain suitable for longer reach applications, and references common elements from Recommendation ITU-T G.709.1 and FEC structures from Recommendation ITU-T G.709.3. Edition 2.0 contains the following extensions to Edition 1.0: Add FlexO skew to scope of clause 10 Add new 1.6T and 1.2T long reach interfaces with OFEC and probabilistic constellation shaping in clause 13. Correct Figure 8-1 Fixed typo in Table 12-3 Added digital sub-carrier nomenclature to clause 11 and 12 Corrected some typos in clause 12.4.2