Building Windsurf with Varun Mohan

What happens when LLMs meet real-world codebases? In this episode of The Pragmatic Engineer, I am joined by Varun Mohan, CEO and Co-Founder of Windsurf. Varun talks me through the technical challenges of building an AI-native IDE (Windsurf) and how these tools are changing the way software gets built. We discuss: • What building self-driving cars taught the Windsurf team about evaluating LLMs • How LLMs for text are missing capabilities for coding like “fill in the middle” • How Windsurf optimizes for latency • Windsurf’s culture of taking bets and learning from failure • Breakthroughs that led to Cascade (agentic capabilities) • Why the Windsurf teams build their LLMs • How non-dev employees at Windsurf build custom SaaS apps – with Windsurf! • How Windsurf empowers engineers to focus on more interesting problems • The skills that will remain valuable as AI takes over more of the codebase • And much more! — Brought to by: •⁠ Modal⁠ — The cloud platform for building AI applications https://modal.com/pragmatic •⁠ CodeRabbit⁠⁠ — Cut code review time and bugs in half. Use the code PRAGMATIC to get one month free. https://www.coderabbit.ai/ — The Pragmatic Engineer deepdives relevant for this episode: • IDEs with GenAI features that Software Engineers love https://newsletter.pragmaticengineer.com/p/ide-that-software-engineers-love • AI tooling for Software Engineers in 2024: reality check https://newsletter.pragmaticengineer.com/p/ai-tooling-2024 • How AI-assisted coding will change software engineering: hard truths https://newsletter.pragmaticengineer.com/p/how-ai-will-change-software-engineering • AI tools for software engineers, but without the hype https://newsletter.pragmaticengineer.com/p/ai-tools-for-software-engineers-simon-willison — Where to find Varun Mohan: • X: https://x.com/_mohansolo • LinkedIn: https://www.linkedin.com/in/varunkmohan/ Where to find Gergely Orosz: • X: https://x.com/GergelyOrosz • LinkedIn: https://www.linkedin.com/in/gergelyorosz/ • Bluesky: https://bsky.app/profile/gergely.pragmaticengineer.com • Newsletter and blog: https://www.pragmaticengineer.com/ — In this episode, we cover: (00:00) Intro (01:37) How Windsurf tests new models (08:25) Windsurf’s origin story (13:03) The current size and scope of Windsurf (16:04) The missing capabilities Windsurf uncovered in LLMs when used for coding (20:40) Windsurf’s work with fine-tuning inside companies (24:00) Challenges developers face with Windsurf and similar tools as codebases scale (27:06) Windsurf’s stack and an explanation of FedRAMP compliance (29:22) How Windsurf protects latency and the problems with local data that remain unsolved (33:40) Windsurf’s processes for indexing code (37:50) How Windsurf manages data (40:00) The pros and cons of embedding databases (42:15) “The split brain situation”—how Windsurf balances present and long-term (44:10) Why Windsurf embraces failure and the learnings that come from it (46:30) Breakthroughs that fueled Cascade (48:43) The insider’s developer mode that allows Windsurf to dogfood easily (50:00) Windsurf’s non-developer power user who routinely builds apps in Windsurf (52:40) Which SaaS products won’t likely be replaced (56:20) How engineering processes have changed at Windsurf (1:00:01) The fatigue that goes along with being a software engineer, and how AI tools can help (1:02:58) Why Windsurf chose to fork VS Code and built a plugin for JetBrains (1:07:15) Windsurf’s language server (1:08:30) The current use of MCP and its shortcomings (1:12:50) How coding used to work in C#, and how MCP may evolve (1:14:05) Varun’s thoughts on vibe coding and the problems non-developers encounter (1:19:10) The types of engineers who will remain in demand (1:21:10) How AI will impact the future of software development jobs and the software industry (1:24:52) Rapid fire round — See the transcript and other references from the episode at https://newsletter.pragmaticengineer.com/podcast — Production and marketing by https://penname.co/. For inquiries about sponsoring the podcast, email [email protected].