Yi-Coder is a series of open-source large language models (LLMs) that deliver state-of-the-art coding performance with fewer than 10 billion parameters. It comes in two sizes—1.5B and 9B parameters—offering base and chat versions designed for efficient inference and flexible training. Yi-Coder-9B has been additionally trained on 24 trillion high-quality tokens from GitHub's code repository-level code corpus and code-related data filtered from CommonCrawl. Yi-Coder excels in various programming tasks, including basic and competitive programming, code editing, repository-level completion, long-context understanding, and mathematical reasoning.