A PCIe retimer includes read-only vendor registers with low latency mode entry and exit values. In-band low latency switching logic monitors the output of an elastic buffer for read commands of the vendor registers and, when such read commands are received, reads the corresponding address and switches a multiplexer between a link training data path and a low latency data path based on the return value of the read operation. Read commands, and therefore control of data path switching, is handled entirely in-band. Return values of the read operations indicate success or failure of mode switching to the root complex.