This Week I Learned - * Anthropic's Claude Code, a closed-source AI coding CLI tool, leaked ~512,000 lines of TypeScript source code on March 31, 2026, via an exposed source map in its npm package, revealing internal architecture, 44 feature flags, and 20 unreleased features; the company responded with DMCA takedowns on original copies. A developer quickly rewrote the codebase in Python using OpenAI's Codex, creating a functional derivative hosted on GitHub that evades copyright claims, amassing 29k stars and 40k forks in hours as an educational open-source alternative. This incident underscores AI's role in accelerating code replication, challenging traditional IP protections for software—Anthropic may overlook enforcement to avoid precedents that could restrict LLM training or generation of similar derived works. * Andrej Karpathy compares LLMs to probabilistic CPUs that handle tokens statistically, in contrast to the traditional deterministic computation based on byte...