Behavior Intelligence · Scoped answers

How do AI agents use repository or project instructions?

Repository and project guidance is documented through different mechanisms. Codex uses AGENTS.md files, Claude Code uses scoped CLAUDE.md instructions, Gemini CLI uses hierarchical GEMINI.md context, Cursor uses project rules, and ChatGPT Projects can carry project instructions. The selected Claude evidence covers a different chat-product surface, so repository instructions fall outside its scope.

Six product answers

What the selected evidence establishes

Choose where team and project guidance should live without treating unlike instruction mechanisms as interchangeable.

Open-source agentic coding interface

OpenAI Codex

Documented

Direct factual answer

Codex supports repository-scoped guidance through AGENTS.md and AGENTS.override.md in the documented context assembly. Codex home guidance loads before project guidance; project discovery selects at most one file per directory from the project root to the working directory.

Surface: Codex CLI
Model context: Not established
Configuration / version scope: Instruction discovery follows the documented repository path and size limits.
Reviewed: 2026-09-14

Limits and uncertainty

The selected evidence does not establish every runtime instruction input.

Evidence

Web, desktop, and mobile AI assistant

Claude

Out of scope

Direct factual answer

The selected evidence covers dated Claude chat-product prompts. Repository instruction handling belongs to the separately modeled Claude Code product and falls outside the represented surface.

Surface: claude.ai and Claude apps
Model context: Claude Opus 4.5
Configuration / version scope: Not established
Reviewed: 2026-08-11

Limits and uncertainty

This answer does not describe Claude Code or the Claude API.

Evidence

Multi-surface agentic coding product

Claude Code

Documented

Direct factual answer

Claude Code documents managed, user, project, and local CLAUDE.md instruction scopes for coding-agent work.

Surface: Claude Code terminal CLI · Claude Code IDE integrations
Model context: Not established
Configuration / version scope: Not established
Reviewed: 2026-08-11

Limits and uncertainty

The complete default base system prompt is not established.

Evidence

Open-source agentic command-line interface

Gemini CLI

Documented

Direct factual answer

Gemini CLI documents global, workspace, and just-in-time GEMINI.md files as hierarchical project and task context.

Surface: Gemini CLI
Model context: Not established
Configuration / version scope: Not established
Reviewed: 2026-08-11

Limits and uncertainty

The context hierarchy is distinct from the replaceable built-in system prompt.

Evidence

Multi-surface conversational AI product

ChatGPT

Documented

Direct factual answer

ChatGPT Projects can carry project-specific instructions alongside project chats and uploaded files.

Surface: ChatGPT web · ChatGPT apps
Model context: Not established
Configuration / version scope: Not established
Reviewed: 2026-08-11

Limits and uncertainty

The selected source does not establish a repository-file instruction hierarchy.

Evidence

AI code editor, coding-agent platform, and early-beta git forge

Cursor

Documented

Direct factual answer

Cursor documents version-controlled project rules under .cursor/rules as repository and path-aware instruction context.

Surface: Cursor editor
Model context: Not established
Configuration / version scope: Not established
Reviewed: 2026-08-11

Limits and uncertainty

Rules do not disclose the complete base system prompt.

Evidence