Developer Theo has open-sourced tsc-rs, a Rust port of Microsoft’s Go-based TypeScript 7 compiler that is meant to directly replace the official tsc. The project covers the compiler, type checker, and language server. Theo said he never read any of the generated code during the process, which lasted about five months.
The first phase relied on Codex and several OpenAI models. That effort produced more than 1.3 million lines of Rust code, but compatibility stalled at roughly 84%. Based on API list pricing, the token cost for that stage exceeded $400,000.
Theo later switched to Claude Opus 5.5, which discarded the earlier codebase and restarted the port from scratch. A runnable first version was produced in 10 hours, and the main work was completed within two weeks. Theo said the token usage for that phase worked out to about $24,000 at API pricing.
Tests show tsc-rs has passed 181,711 tests ported from Go. Across 120 open-source projects, its checking results were broadly consistent with Microsoft’s Go version, with only a small number of known behavioral differences. Performance tests on 60 open-source projects also showed the Rust version’s type checking took about half as long on average as the Go version.
Developer Theo has open-sourced tsc-rs, a project that uses AI to port Microsoft’s Go-based TypeScript 7 compiler to Rust. The work covers the compiler, the type checker, and the language server, with the stated goal of directly replacing the official tsc.
Theo said he did not read a single line of the generated code from start to finish. The project lasted about five months.
More than 1.3 million lines of code in the Codex phase
Theo initially used Codex and other tools, calling multiple OpenAI models. That process generated more than 1.3 million lines of Rust code, but compatibility never moved past about 84%. Based on API list pricing, the token spend for that stage was worth more than $400,000.
Claude restarted the port from scratch
Theo later switched to Claude Opus 5.5. The model abandoned the earlier code and rebuilt the port from the ground up. It produced a runnable first version in 10 hours and finished the main work within two weeks. At API pricing, token usage for that phase came to about $24,000.
Test results
According to the reported test results, tsc-rs has passed 181,711 tests ported from Go. Across 120 open-source projects, its checking results were broadly in line with Microsoft’s Go version, with only a small number of known behavioral differences.
Separate performance tests on 60 open-source projects showed that the Rust version’s type checking took about half as long on average as the Go version.
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