microsoft/TypeScript

Choose this fork only if you specifically need ExtJS-compatible class emission on an old TypeScript 1.8 baseline. For anything else, upstream TypeScript is the better default because this fork is heavily outdated and materially behind current compiler, tooling, and maintenance work.

Prefer this fork only if you need Bloomberg's historical branch state or internal collaboration workflow. For normal TypeScript development, tooling, or adoption, upstream is the better default because this fork is stale and significantly behind.

Choose this fork only if you already depend on its historical customizations. For new work or general TypeScript use, upstream is the safer choice because this fork is stale and far behind current maintenance.

Prefer this fork only if its custom TypeScript semantics are the product requirement. If you want current fixes, lower maintenance risk, or mainstream compatibility, upstream is the better default.

Choose the fork only if you need its legacy compiler/test behavior or its bespoke automation. If you want current TypeScript, this fork is too stale and too far from upstream to be a low-risk starting point.