Anthropic-developed JavaScript runtime Bun released a new version, Bun v1.4.3, on October 10, 2026. The headline feature is a TypeScript type checker available through the built-in “bun check” command. Bun says it is more than three times faster than TypeScript 7, which is implemented in Go, while also using less memory.
Bun Takes On Checking as Well as Execution
First, a little background. Type checking is a process that catches mistakes in how code is used before a program runs—for example, passing a string where a number is expected. It is one of TypeScript’s major selling points and an essential step in larger-scale development.
In addition to JavaScript, Bun can load and transpile TypeScript files, then run them directly. Separately, it can check TypeScript files for type errors when they are passed to the “bun check” command. In this update, the speed of the latter feature takes center stage.
When the tools for running and checking code are brought together in one environment, developers can reduce both the number of tools they need to adopt and the effort involved in configuring them. This update reflects a broader trend: runtimes are expanding their role from places to run code to places that also handle safety checks during development.
Compatibility Numbers Show It’s About More Than Speed
A type checker is of little use if it is fast but produces results that diverge from the original. On this point, the release notes say the checker passed 100% of TypeScript 7.0.2’s conformance tests.
Bun also says it checked 72 major open-source TypeScript files with both TypeScript and Bun and compared the results. The set included files with errors deliberately introduced by the Bun team, and the results differed in just one place. The figures suggest an effort to demonstrate how closely Bun’s checks align with TypeScript’s.
For developers considering a switch, this may matter just as much as speed. Even if checks run faster, changes in the warnings they produce could affect a team’s workflow.
How to Read the “More Than 3x Faster” Claim
Bun says its type checker is more than three times faster than TypeScript 7 and uses between half and one-quarter—or even less—of the memory. TypeScript 7 has already been sped up through its Go implementation, so Bun is claiming to significantly outperform an already-fast checker.
However, these are comparison results reported by Bun. The time required for type checking varies with the size and style of the code and the machine running it. How much time developers will save on their own projects will only become clear when they try it in practice.
Even so, shorter wait times can make it easier to run checks every time a file is saved or to check frequently while editing. Lower memory usage should also make the checker easier to use in resource-constrained environments such as CI. The speed figures could have an impact on the development process itself.
Other Updates Beyond Type Checking
Version 1.4.3 includes many other changes. According to the official announcement, the release fixes 166 issues and cuts server CPU usage while idle by 67%.
Other changes include improved compatibility with Node.js, faster JSON.parse, and numerous bug fixes. The type checker is the star of the release, but the update also brings improvements across the runtime. See the release notes on Bun’s official blog for details.
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