As the cost of GPUs continues to rise, GPU-sharing solutions have become increasingly important for improving efficiency and maximizing resource utilization. At the same time, large-scale operational deployments of such solutions remain relatively less explored, especially in heterogeneous production environments where workload dynamics and orchestration complexity introduce new practical considerations. In this paper, we introduce eGPU, an elastic, efficient, and scalable GPU-sharing framework tailored for production-scale concurrent machine learning (ML) training and inference. eGPU enables fine-grained, runtime-adjustable sharing of GPUs across multiple jobs, while preserving high resource utilization and fault isolation. To address communication bottlenecks, eGPU supports native NVLink/NCCL-based communication between shared GPU instances, capabilities that are limited or unavailable in many existing designs. Built with production deployment in mind, eGPU integrates with Kubernetes (K8s) to support large-scale orchestration. It has been deployed and running stably in production clusters with over 10,000 GPUs for five years. Our evaluation results show that eGPU achieves elastic and precise control over instance sizes, improves job efficiency by 21% to 31% than SOTA sharing solutions, saves the number of GPUs required by up to 8×, and improves cluster GPU utilization by more than 3×.