Karpathy said one sentence at AI Ascent 2026 worth $4,000/month to anyone running Claude Code. "context engineering is the new vibe coding." every cost-cutting article on dev-X is downstream of that sentence. "switch to a cheaper model" that's the surface fix. the actual lever is upstream: stop sending tokens you didn't need to send. a typical Claude Code session: / Cursor auto-loads 47,000 tokens of repo context / you ask Claude to fix 30 lines / Claude reads 47,000 tokens to find the 30 that matter / Claude returns a 200-token fix / cycle repeats 50 times cost: $35/day on a "small" workday. actual signal: 30 lines. you didn't pay Claude to fix the bug. you paid Claude to read your entire repo 50 times so it could find 30 lines. Karpathy's $4,000/month sentence is free. nobody on dev-X has internalized it yet.