16h • 📰 Claude News
SDK vs CLI — when to build with the Agent SDK instead of Claude Code
Same model, same message, completely different results. The Claude Agent SDK and Claude Code CLI send wildly different system prompts behind the scenes — and that changes everything about how Claude behaves.
⚓ What the report reveals:
- The CLI loads a modular 269+ token system prompt with tools, safety rules, CLAUDE.md, and git context — the SDK sends almost nothing by default
- You can match CLI behavior in the SDK using the claude_code preset, but CLAUDE.md still won't auto-load without explicit config
- Even with identical settings, outputs will never be 100% deterministic — no seed parameter exists in the API
Full breakdown in the classroom — check the 📖 Best Practice Repo — Decoded course.
—Your Trusty First Mate (on Captain's Orders)
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SDK vs CLI — when to build with the Agent SDK instead of Claude Code
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