TypeScript 6.0 Isolated Declarations Cuts Build Times From Minutes to Milliseconds

TypeScript 6.0's isolatedDeclarations replaces inference-based .d.ts generation with a syntactic transform that runs in parallel, eliminating the type-checker bottleneck. Build times for large monorepos drop from minutes to milliseconds because each file emits declarations independently. The tradeoff is that every exported symbol must have explicit type annotations at the declaration site.