This house has a brain, and it forgets on purpose

Your smart speaker executes commands. This thing understands intent, and the gap between those two sentences is the whole sighting.

Ziggy is a home AI assistant built by one engineer, and instead of the usual chatbot-with-plugins shape, it is architected like a biological brain. The writeup names the parts like a neurology textbook and then shows you the stack behind each one.

Five regions, each with a job

Requests hit a triage agent that routes like a prefrontal lobe deciding which region handles the job. The metaphor is load-bearing: every request enters through that agent, and nothing reaches a deeper system without being routed first.

Behind it sit four more regions. A motor cortex of tool servers drives the physical house, lights, climate, anything on the network. A hippocampus holds long-term memory. A cerebellum, in practice a cron-driven scheduler, handles recurring automation. A temporal lobe sends notifications and check-ins over SMS.

The builder's degree mixes psychology and neuroscience; the day job is distributed systems. The brain diagram is not decoration. It is autobiography.

The stack under the metaphor

FastAPI serves the backend. Haystack orchestrates the multi-agent routing, with Anthropic models doing the reasoning at each step. The tool layer speaks the Model Context Protocol, the open standard for wiring AI systems to external tools, through FastMCP servers, and three of Ziggy's MCP servers are purpose-built: one for the memory graph, one for scheduling, one for SMS.

Conversations persist to MongoDB. A Next.js client streams answers over WebSocket and shows which cortex is working while you wait. Every model call is traced through Opik, with the logs landing in an ELK stack, so a bad answer is a debuggable event instead of a mystery. This is a hobby project instrumented like a bank.

It is also stateless enough to run almost anywhere: AWS Lambda, Azure Container Apps, or a few pods on the builder's own five-node k3s cluster, the same scavenged-hardware machine from the datacenter in the hallway. It runs on that cluster today, next to the rest of the house's infrastructure.

Memory that forgets on purpose

The part that made me put my coffee down. Ziggy remembers with a Neo4j graph plus embeddings, and every conversation moves through three stages. First a summary: a title under ten words, a body under 250. Then consolidation: episodic memories, what happened, and semantic memories, what is true, get extracted and linked into the graph, threaded back to the conversation that produced them. Then, deliberately, forgetting. Stale information gets pruned, and the pruning leaves an audit trail of what was removed and why.

Most chat memory is a transcript, and a graph that only grows becomes noise. A home assistant with a documented forgetting policy is a sentence I did not expect to type this year. Most billion-dollar products cannot tell you what they remember about you. This one can tell you what it chose to stop remembering, and when.

What runs today, and what is still on paper

The routing, the memory pipeline, the MCP tool layer, and the device control all run now. A visual cortex is still on paper: SR501 presence sensors, so the house knows who is in the room rather than just what they typed. Splitting each cortex into its own container is the other open item, for blast-radius reasons, once more of the house depends on this staying up. The brain metaphor is still growing new lobes.

The design line that sums it up comes straight from the writeup: understand intent, not follow commands.

One person built this, wrote it up, and put the reasoning where anyone can check it. That is the kind of thing this site exists to point at. Go read the full home automation build writeup. If you want to try the routing pattern yourself, Haystack's own tutorials walk through building a tool-calling agent and then a multi-agent system, which is exactly the shape of Ziggy's front door. And the same builder once handed an AI the doors on purpose, as a game: the AI runs the doors.

The house is thinking.