More than 1.2 million developers signed up to use the GitHub Copilot preview over the past 12 months, and it will remain a free tool for verified students and maintainers of popular open-source projects. In files where it’s enabled, GitHub says nearly 40 percent of code is now being written by Copilot.

Priced at $10 per month or $100 a year, GitHub Copilot is capable of suggesting the next line of code as developers type in an integrated development environment (IDE) like Visual Studio Code, Neovim, and JetBrains IDEs

With Copilot, developers can cycle through suggestions for Python, JavaScript, TypeScript, Ruby, Go and dozens of other programming languages and accept, reject or manually edit them. Copilot adapts to the edits developers make, matching particular coding styles to autofill boilerplate or repetitive code patterns and recommending unit tests that match implementation code.

Owing to the complicated nature of AI models, Copilot remains an imperfect system. GitHub said that it’s implemented filters to block emails when shown in standard formats, and offensive words, and that it’s in the process of building a filter to help detect and suppress code that’s repeated from public repositories. But the company acknowledges that Copilot can produce insecure coding patterns, bugs, and references to outdated APIs, or idioms reflecting the less-than-perfect code in its training data.