The Chinese Academy of Sciences (CAS) started the routine generation of multi-GNSS differential code biases (DCBs) since the third quarter of 2015. In this contribution, the recent multi-GNSS activities on code bias estimation and analysis at CAS are presented. For multi-GNSS code bias handling, the concept of observation-specific bias (OSB) is introduced in our local (modified triangular series function) and global (spherical harmonics) ionosphere analysis. Three different sets of local or global GNSS tracking networks, including EPN, IGS and MGEX, are used to generate the respective satellite and receiver OSBs, and to check the influences of legacy and new signals, different sets of receivers and tracking networks on the estimation of multi-GNSS OSBs. The OSB results are provided in the new Bias-SINEX Format Version 1.00 and available from our ftp archive (ftp://ftp.gipp.org.cn/product/). For long-term analysis of multi-GNSS OSBs, a practical alignment procedure is proposed to remove the reference datum offset of day-to-day OSB solutions. In addition to the routine generation of weekly and monthly OBS solutions, the long-term variation and stability of satellite and receiver code biases are also analyzed based on the aligned OSB results.