OpenCTI is an open-source cyber threat intelligence platform that ingests, manages, and analyzes threat data using the STIX 2.0/2.1 standard. The system is a monorepo containing a Node.js/TypeScript GraphQL backend (opencti-graphql), a React/Relay frontend (opencti-front), a Python client library (client-python), and a Python worker service (opencti-worker). The backend uses Elasticsearch/OpenSearch as its primary data store, Redis for caching and pub/sub, RabbitMQ for connector queues, and PostgreSQL for migrations. The frontend provides full CRUD UIs, dashboards, workspaces, playbook automation, and workflow management. Key entry points include the GraphQL API (resolvers per entity type), the frontend React app with Relay data fetching, and the Python client for programmatic access. Data flows involve ingestion via CSV/JSON/TAXII/RSS feeds, manual creation, connector enrichment, and inference rules that automatically derive relationships. External dependencies include Elasticsearch, Redis, RabbitMQ, MinIO/S3 for file storage, and optional AI services. The platform supports enterprise features (playbooks, PIR, XTM Hub) gated by license checks.