Sovereign AI deployments often require foundation models to operate under constraints overlooked by standard benchmarks: adherence to legislation, multilingual and multimodal grounding in local contexts, institution-specific safety behaviors, and on-premises deployment on power-constrained infrastructure. We present a production case study detailing the multi-stage engineering pipeline that spans trillion-token-scale continued pretraining, multi-billion-token alignment and post-training for a 123B-parameter natively multimodal foundation model, *Phoenix-VL 1.5 Medium*, optimized for Singapore public-sector use. On our novel localized evaluation suite and behavioral safety framework, the model substantially improves localized multimodal, statutory, and public-safety capability (a +0.118 average gain over the strongest baselines) while retaining broad general capability. We also share empirical analysis from a full production deployment currently serving over 30,000 users and processing ∼1 billion tokens over a two-month period. Ultimately, our findings demonstrate that sovereign AI is best approached as an end-to-end systems problem, where data curation, domain training, institutional alignment, and hardware layout interact and cannot be optimized in isolation.