VieNeu-TTS is a production-grade Vietnamese/English text-to-speech system with instant voice cloning, designed for on-device inference. It provides a Python SDK (vieneu) with multiple model backends (v3 Turbo 48kHz PyTorch/ONNX, v3 Nano CPU, legacy v1/v2), a Gradio web UI (VieNeu-TTS Studio) for single/multi-speaker synthesis, SRT subtitle dubbing, and voice cloning with persistent user profiles. An OpenAI-compatible streaming API server (FastAPI) exposes POST /v1/audio/speech, voice enrollment, and health endpoints, deployable via Docker with CPU/GPU profiles. The architecture follows a factory pattern dispatching to backend-specific engines, with shared utilities for text chunking, audio joining, and voice management. External dependencies include PyTorch/ONNX Runtime for inference, MOSS-Audio-Tokenizer-Nano codec, sea-g2p phonemizer, and Hugging Face model hub for checkpoints. The repository also includes LoRA fine-tuning scripts for custom voice adaptation, extensive test coverage, and CI/CD pipelines.