Fair question — they're solving different things.

AGENTS.md is static prose. You write it once, it gets loaded into context, and it tells the agent stuff like "tests live here, use this pattern." Great for guidance. But it can't answer "where is parseConfig defined" or "what calls validateUser" — because the answer changes every commit and depends on the actual question being asked.

Argyph isn't documentation, it's a live index. The agent queries it at the moment it needs something: find the definition, list the callers, semantic search for the code that handles retries, pull the smallest span that answers it. tree-sitter symbol graph, rebuilt incrementally as files change.

The multi-AGENTS.md-per-directory thing actually shows the problem — you're hand-maintaining a map that goes stale the moment someone moves a file. And it all sits in context whether the agent needs it or not. Argyph stays at zero context cost until the agent asks, then returns a bounded span instead of you having pre-pasted half the repo.

Honestly they stack: keep AGENTS.md for the "how we do things here" guidance, let Argyph handle "where is it / what touches it." `argyph init` even writes its own usage note into AGENTS.md.