The a16z Show Building APIs for Developers and AI Agents
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Sep 6, 2025 Alex Rattray, founder of Stainless and former Stripe developer, chats with Jennifer Li about the evolving world of APIs and SDKs. He underscores the importance of creating high-quality, idiomatic libraries for both developers and AI agents. The duo explores the Model Context Protocol and how it reframes APIs for AI interaction. They discuss the challenges of designing tools for large language models, as well as the critical role of context management and documentation. Rattray predicts a future where every company acts as an API powerhouse.
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From Stripe Docs To A Developer Platform
- Alex Rattray describes building Stripe's API docs and a codegen system that produced idiomatic SDKs from OpenAPI specs.
- He founded Stainless to sell that platform experience to other companies who need polished SDKs and docs.
SDKs Become The Developer-Facing API
- A high-quality SDK often is the API for developers because it shapes their day-to-day experience.
- Polished, idiomatic libraries (types, editor docs, async patterns) matter more than raw REST surfaces.
MCP Makes Models First-Class Users
- MCP reframes APIs as interfaces for LLMs, making SDK-like clients the primary integration path for agents.
- We need to ask what is idiomatic and usable to a model, not just to a human developer.