An event represents a single tracked interaction for a specific agent version and person. Every LLM call or wrapped execution results in exactly one event. Events are the top-level unit used for analytics, logging, and debugging.

An event session represents a full conversation or workflow across multiple events. It is identified by a unique ID, such as a UUID or conversation ID, and groups related events together even if the underlying message history changes over time.

Events contain the messages exchanged during the interaction. This includes user inputs, system prompts, and model responses. Messages are stored in order and represent the exact content sent to and returned from the model.

Each event is associated with a fingerprint. A fingerprint captures environment details such as language, runtime version, SDK versions, and system information. This ensures reproducibility and helps diagnose differences across environments.