The 400G optical module is an optoelectronic conversion module with a transmission rate of micro-400G. Together, they ensure resilient data center interconnectivity and empower. PAM4 (4-Level Pulse Amplitude Modulation): This is the predominant modulation technique used in 400G modules. PAM4 allows each symbol to represent two bits of information, effectively doubling the data rate compared to traditional NRZ (Non-Return-to-Zero) modulation 1. Multi-Mode Fiber (MMF):. Among the emerging standards, the 400G QSFP112 optical transceiver stands out not simply as a higher-speed module, but as a strategic enabler designed around electrical efficiency, advanced modulation, long-reach flexibility, and rack-scale scalability. In this article, we first review the current status of 400GBASE client-side optics standards and multi-source agreements (MSAs).