Anthropic just deleted over 80% of Claude Code’s system prompt for Opus 5, and the model got MORE intelligent, not less.
Fresh off the Opus 5 launch, Claude Code creator Boris Cherny sat down with YC at Startup School 2026 and laid out the exact playbook for building products when the model keeps outrunning them.
We went through the full 36 minutes and pulled out every stealable move (the ablation method, SKIP - not a real violation, higher-level prompting, dynamic workflows that spawn thousands of agents) so you can rebuild your AI product for Opus 5 without watching a second of it.
In this guide you’ll find:
Why Opus 5 Runs for Weeks With No Scaffolding and Ignores Prompt Injection
The Delete Playbook: Cut 80% of Your System Prompt and Rebuild It Line by LineProduct Overhang: The Model Capabilities Startups Aren’t ShippingGive Claude Harder Tasks Than You Think It Can Do: Bun’s Zig-to-Rust Rewrite in 11 DaysVerification Is the Skill Nobody Gets Right: The Two-Week Prompt That Live-Blogged ItselfSpawn Thousands of Agents From One Prompt: Dynamic Workflows and Self-Maintaining Codebases
👋 Just a quick note before you continue!
If you are serious about building or investing in AI, you can subscribe here: Here’s a good place to start:
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Try premium free for 7 days. Or get 50% off this week only. Cherny frames the launch with one data point: Anthropic took Arc AGI to 30%, “before the best score was in the low single digits or low teens.” Everything below is his account of how to build products for a model moving that fast.