Anders Hejlsberg Shares 7 Critical Learnings from Building C# and TypeScript

Quick Brief

• The Release: GitHub published an exclusive technical interview with Microsoft Technical Fellow Anders Hejlsberg on January 27, 2026, detailing seven architectural learnings from C# and TypeScript development
• The Impact: Insights target C-level executives, developers, and language designers navigating modern software scaling challenges and open source tool development
• The Context: Published as TypeScript claimed the #1 ranking on GitHub in August 2025, reinforcing Hejlsberg’s influence across two decades of programming language evolution

GitHub released an exclusive technical profile featuring Anders Hejlsberg, the Microsoft Technical Fellow and architect behind C#, TypeScript, Delphi, and Turbo Pascal, on January 27, 2026. The interview examines seven foundational learnings centered on fast feedback loops, scaling enterprise software, open source visibility, and developer tool design drawn from Hejlsberg’s 25-year tenure at Microsoft.

Anders Hejlsberg joined Microsoft in 1996 after creating Turbo Pascal and serving as chief architect of Borland’s Delphi. At Microsoft, he designed the J++ language and Windows Foundation Classes before becoming lead architect of C# in 2000. In 2012, Hejlsberg launched TypeScript as a typed superset of JavaScript, addressing scalability challenges in large codebases without abandoning the JavaScript ecosystem.

Hejlsberg currently holds dual roles as C# lead architect and TypeScript core developer, making him one of the few engineers to maintain active leadership across two major programming languages simultaneously. TypeScript reached #1 usage ranking on GitHub in August 2025, surpassing JavaScript and Python in repository adoption.

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Core Learnings: Fast Feedback Loops and Scaling Infrastructure

The GitHub interview highlights Hejlsberg’s emphasis on fast feedback loops as a non-negotiable requirement for modern developer tools. This principle directly influenced TypeScript’s compiler architecture, where incremental compilation and real-time type checking deliver sub-second feedback in editors like Visual Studio Code. The TypeScript team announced Project Corsa in March 2025, a native code port achieving 10x compilation speed improvements to address scaling demands in enterprise monorepos.

Hejlsberg identifies open source visibility as a transformative factor distinguishing TypeScript from C#. All TypeScript development occurs in public GitHub repositories, enabling community contributions and immediate issue tracking. This contrasts with C#’s early closed development model, though .NET transitioned to open source in 2014.

Technical Architecture Lessons from Two Decades

Hejlsberg highlights C#’s reified generics implementation as a critical architectural decision, contrasting with Java’s erasure-based approach that loses type information at runtime. However, he identifies nullable reference types as C#’s largest design regret, requiring a 20-year retrofit to add non-nullable annotations.

AdwaitX Analysis: The Shift to Developer Experience as Competitive Advantage

Hejlsberg’s dual language stewardship reveals a strategic pivot from runtime performance to developer productivity. C# prioritized execution speed and enterprise features through the CLR, while TypeScript eliminates runtime overhead entirely by compiling to JavaScript. This architectural choice enabled TypeScript to integrate seamlessly with existing JavaScript toolchains, lowering adoption friction.

The native TypeScript compiler rewrite demonstrates Microsoft’s commitment to maintaining performance parity with compiled languages. Microsoft’s official benchmarks show the new compiler reduces build times from 77.8 seconds to 7.5 seconds for a 1.5 million line Visual Studio Code codebase. This addresses enterprise scaling bottlenecks where incremental compilation times directly impact developer feedback loops.

Open source visibility emerged as TypeScript’s strategic differentiator, with Hejlsberg’s GitHub profile showing 294 contributions in the last year, including direct compiler fixes and control flow analysis improvements. This public development model contrasts sharply with C#’s initial closed-source approach, validating transparency as a growth accelerator for modern programming languages.

Roadmap: Native Compiler Deployment and AI Integration

Microsoft announced Project Corsa the TypeScript native compiler port in March 2025, with preview builds available as of December 2025. The Go-based implementation removes Node.js dependency and runs as a standalone binary, focusing on build performance rather than runtime speed.

Hejlsberg’s team is exploring AI-assisted type inference to reduce annotation burden in large TypeScript codebases. This initiative aligns with Microsoft’s broader Copilot integration strategy, where language services provide context for code generation models.

The C# roadmap prioritizes discriminated unions and pattern matching enhancements, borrowing concepts from functional languages to improve type safety. These features address community requests for more expressive type systems without abandoning C#’s imperative foundations.

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