Apparatus and methods for implementing high-speed Ethernet links using a hybrid PHY (Physical layer) selectively configurable to employ a non-interleaved RS-FEC (Reed Solomon Forward Error Correction) sublayer or an interleaved RS-FEC sublayer. An adaptive link training protocol is used during link training to determine whether to employ the non-interleaved or interleaved RS-FEC during link DATA mode. Training frames are exchanged between link partners including control and status fields used to respectfully request a non-interleaved or interleaved FEC mode and confirm the requested FEC mode is to be used during link DATA mode. The hybrid PHY includes interleaved RS-FEC and non-interleaved RS-FEC sublayers for transmitter and receiver operations. During link training, a determination is made to whether a local receiver is likely to see decision feedback equalizer (DFE) burst errors. If so, the interleaved FEC mode is selected; otherwise the non-interleaved FEC mode is selected or is the default FEC mode. The apparatus and methods may be implemented for 100 GB ASE-CR1 and 100 GB ASE-KR1 Ethernet links and interfaces.