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fairseq2 is a modern, modular sequence modeling framework developed by Meta AI Research as a complete redesign of the original fairseq library. Built from the ground up for scalability, composability, and research flexibility, fairseq2 supports a broad range of language, speech, and multimodal content generation tasks, including instruction fine-tuning, reinforcement learning from human feedback (RLHF), and large-scale multilingual modeling. Unlike the original fairseq—which evolved into a large, monolithic codebase—fairseq2 introduces a clean, plugin-oriented architecture designed for long-term maintainability and rapid experimentation. It supports multi-GPU and multi-node distributed training using DDP, FSDP, and tensor parallelism, capable of scaling up to 70B+ parameter models. The framework integrates seamlessly with PyTorch 2.x features such as torch.compile, Fully Sharded Data Parallel (FSDP), and modern configuration management.
Features
- Composable and deterministic configuration system
- High-throughput C++ streaming data pipeline for text and speech
- Recipes for instruction fine-tuning, preference optimization, and RLHF
- Native vLLM integration for optimized generation and inference
- Supports 70B+ parameter models with DDP, FSDP, and tensor parallelism
- Modular, next-generation fairseq with a clean, extensible architecture
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