What is Muse Code, Meta's new AI agent for large codebases

Meta has announced Muse Code, a new AI agent designed to help developers work with large and complex software repositories. The company says the tool aims to address the biggest weakness of earlier-generation coding assistants: their inability to understand the context of an entire codebase.
Most existing AI coding tools can only process a handful of files, or a limited context window, at a time. That means when developers work in large repositories containing thousands of files, suggestion quality tends to drop and the tool can propose inconsistent changes.
Muse Code, according to Meta, works by mapping the dependencies between files across a repository and dynamically updating that map during a query. This approach is designed to let the tool better predict how a change made in one function might ripple elsewhere in the project.
The company claims the tool performs especially well on large-scale refactoring tasks — restructuring code without changing its behavior. These tasks have traditionally been particularly challenging for AI assistants, since they require consistent changes across numerous files simultaneously.
Meta says Muse Code has been tested internally for months and is already used across the company's own large-scale codebases. The company argues this internal use helped the tool mature under real-world conditions before its wider release.
The tool integrates with Meta's previously announced Muse Spark platform, an integration the company says allows code suggestions to draw on its broader AI infrastructure. Meta states the two products are designed to work together to boost developer productivity.
Rival companies are developing similar 'repository-level awareness' approaches; the industry overall is shifting from single-file-focused coding assistants toward tools that understand full project context.
Security experts note that this kind of tool requiring broad access to large codebases can introduce new risks, particularly concerns about sensitive or proprietary code leaking into external systems. Meta emphasizes that data stays within the company and is not transferred externally.
Developer communities have not yet independently tested the tool's real-world performance; early access is currently limited to a small group of external developers. Meta says it plans to gradually expand access based on feedback.
Analysts note that AI tools capable of understanding large codebases could deliver a meaningful productivity boost in software development, though the reliability of these tools at scale still needs to be proven.
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