Why an AI Agent's True Identity Lives in Its Event Log, Not Its Runtime

A new perspective in AI development argues that an agent's core identity is defined not by its model or runtime, but by its append-only log of events — every input, output, tool call, and result it has accumulated. This log, combined with a session definition covering system prompts and tool descriptions, constitutes the agent's complete and durable state. Because any fresh executor can read the same log and resume exactly where the agent left off, the architecture becomes fault-tolerant and easier to reason about. The model, tools, and runtime are recast as mere interpreters that read from and write to this central record, mirroring how databases use an underlying change log to drive all other projections. Compaction, which summarizes older history to fit finite context windows, is treated as a lossy fork rather than a replacement, since discarding the raw log means permanently losing part of the agent's state.