Circuit is a substrate-agnostic interface for directing distributed intelligence. Currently pointed at building iOS apps, but architected to be overlaid directly onto iOS itself, it makes a clean break with the IDE: Circuit never shows the user code, and never speaks in software-engineering concepts. Behavior is the artifact. The Director composes in plain language and watches the system work. Her role is to attend to what orchestration cannot: discretion, intuition, effects in reality, the texture of how a thing sits in someone's life. Questions that bear on those dimensions surface as escalation cards in TCGHand, an idiom borrowed from Trading Card Games. Cards arrive in a carousel where they can be answered, flicked off the top of the screen, or held and dragged back down to hand the decision to the orchestrator. Choosing when to hold a card is as important as choosing the moment to play it, because once Circuit's substrate is genericized past app-building, the order in which the cascade takes its actions in the world becomes a primary design decision.

Cascade SDK is the orchestration engine. The Director's Concierge instantiates agents not like contracted workers but appendages, given mid-range tasks before merging back to turn over their work and memories; both orchestrator and agents can in turn spawn sub-agents specialized for in-line planning, exploration, critique, consolidation, and building. The architecture is evolved from Kubernetes, the distributed structure of Git, and modern R&D organizations, and scales horizontally and vertically by the same logic. But Cascade SDK's core identity isn't its topology: it's the carefully inscribed space of human-AI co-participation that the architecture makes possible. The orchestrator's deference to the Director is epistemic, not hierarchical: it defers because it literally cannot perceive what the Director perceives. Escalations exist to acquire information the orchestrator lacks. This principle is integrated at the level of prompt and architecture rather than tacked on as policy, because language is the primary interface for shaping a model's space of intent, and crafting that space is what intelligence design, as a nascent discipline, is about.

Circuit v2 is where the architecture caught up with the interface. The canonical toy model built January 2026 both lacked and quite naturally necessitated some basis for cascade memory. v2 supplied it: a continuously revised markdown StateDocument, lifted out of the view layer to serve as the cascade's working memory, with the run's surface rebuilt around it as a Dashboard, resulting in an interface and architecture which are unified and magically paper-like from top to bottom. Seventy-six of its hundred commits touch the SDK: by the end, the app existed to exercise the runtime rather than the reverse. Wound down in March 2026, its essential patterns of an orchestrator delegating to disposable sub-agents over a shared graph of traces, deferring to a Director for escalation along some epistemic limit, represent shapes which have since become ubiquitous in agent harnesses.

Circuit, Cascade SDK, and Circuit v2 are archived open source under MIT.