What does this equation mean?

Claude Code executes $a_t$ — subject to a permission check described in the next section — against the real filesystem, shell, or network, producing an observation $o_t$ : a diff applied, a command’s stdout and exit code, a search result. That observation is appended to the context for the next step: $c_{t+1} = c_t \oplus (a_t,\ o_t)$. The loop repeats until $\pi$ emits a stop rather than a tool call. Nothing in this is exotic; it is the standard shape of a tool-using agent. What matters for this article is what each symbol is standing in for in a real, shipped product: $a_t$ is not a hypothetical action but a call to a real interpreter with real side effects on a real machine, $o_t$ is not simulated feedback but the actual return value of that call, and the boundary between “the model decided” and “the harness allowed” is enforced by software, not by the model’s own restraint.