Claude Code is now a $2.5B run-rate product powering 4% of all GitHub commits, anchoring Anthropic's decisive move into Platform through Claude Managed Agents (PaaS at $2.58 fulfillment cost on $1k service, Linear SDK integration), the Advisor Strategy (Opus planning with Sonnet/Haiku execution as first-class pattern), the Monitor tool (event-driven background scripts), /ultraplan (cloud planning with browser review and local CLI back-teleport), Claude Design (Opus 4.7 vision rendering HyperFrames videos in 2 prompts), and official setup/plugin flows. The workflow has matured into a general work operating system: CEOs use it as AI Chief of Staff; Marcus Moretti runs Spiral at Every as one-person PM/code/support/marketing with strategy.md + /ce:product-pulse cron replacing 60% of the old PM week; sales teams run 11-API pipelines through Skills files. Role specialization ships as packages (gstack installs 6-specialist team in 30 seconds) and multi-model loops enable Opus 4.7 planning, GPT-5.5 review, Playwright validation, and @conductor_build model-switching at ~$400/month. Plan files, /handover, structured /goal prompts, premortem flipping ("it's 6 months from now and this is dead"), /ss screenshot skill, and specialized harnesses (designer, marketer, sales, motion, bookkeeper) operate alongside agent-view research (consolidating cross-project coding sessions) and one-command skill promotion (turning personal PM OS into team OS without leaking context). Architecture: plain-text markdown vault + Claude Code engine. Three-file configuration for articulate agents: SOUL.md (constitution—voice/values, brutally specific or reverts to ChatGPT), USER.md (~4000-word user model), AGENTS.md (operational playbook). Cost hierarchy matters: 80% of agent tasks are janitorial, making hierarchical model routing (10x cost reduction) essential. Scratchpad/napkin patterns provide distinct memory compounding across sessions. Obsidian + Claude Code is the community stack; vault pattern extends to git-as-version-history (Tolaria) and scales to teams—four independent implementations (DoorDash, Pendo, Google, solo) converged on the same three-layer team-knowledge architecture, confirming compounding data is the moat, not technology. Design extends from 3-layer harness (Skills + Canvas + Inspiration) to Claude Design + HyperFrames, Codex image generation replacing UI prototyping, Refero's 2,000 DESIGN.md training files, and Lamina Labs' whiteboard animation SDK. Ecosystem: Anthropic investments (11 open-source plugins, free course, 14-min agent guide, 33-page Skills guide, Managed Agents, official setup plugin) + community tooling (gstack, self-improving skills: 32/50 → 47/50 overnight, claude-smart, Evo, GitHub plugin marketplace auto-sync, CodexBar, Decode, FieldTheory, Excalidraw, ByteRover, Tolaria MCPs, NVIDIA 80-model free API, LibreChat wrappers, 1,200+ hour research workflows, voice cloning at 94% accuracy, Codex overflow). Six extension mechanisms (Plugins, Skills, MCPs, Commands, Subagents, Hooks) across three layers: environment (skip-permissions flags, game sound, performance recovery), context architecture (CLAUDE.md <200 lines, tiered manifests), and skill design (state machines, self-improving eval loops). System engineering beats prompt engineering.