Claude Code evolved into a work operating system beyond Research-Plan-Build. Plan-first remains core: plan.md survives context loss, /handover preserves knowledge across sessions, 4-6 parallel Ghostty sessions enable concurrent work. /ultraplan shifts planning to cloud browser (inline comments, visual diagrams). Monitor tool replaces polling with event-driven scripts. Marcus Moretti's PM workflow (strategy.md + daily /ce:product-pulse cron) replaces 60% of traditional PM work. Self-improving skill loops (3-5 binary criteria, 10 runs, score, rewrite) jump from 32/50 to 47/50 overnight. Strong /goal prompts define measurable outcome, context, constraints, verification, rollback, stop rules. Interactive HTML skill offers Google Docs-style commenting for generated pages. Plan-optimizer iteratively scores until noise; particularly effective with Fable 5. Dynamic Workflow mode + Ultracode (xhigh thinking, automatic decisions) send thousands of subagents for complex tasks. Premortem flip cancels optimism on high-stakes decisions. gstack (30-second install) transforms Claude into 6-specialist team: CEO challenges decisions, Designer ships variants, QA runs real tests—Garry Tan's 23-tool setup open-sourced. Multi-LLM workflows (Opus 4.7 plans, GPT-5.5 reviews, Playwright validates) cost ~$400/month. Three-folder architecture (knowledge/projects/people) creates compounding value by Day 90. One-command skill converts personal PM OS into team OS. Fully automated pipelines (Feature Chat → Spec → Implementation → PR → Review) remove humans from execution.