A definition you can take to a budget meeting
An AI aggregator brings multiple model providers into one interface so a person describes an outcome once. Symphony is that interface for Codex, Claude, Gemini and Grok, with a browser dashboard connected to tools on your Mac. Aggregation is the access. Orchestration is the sequence: research, build, independent review, inspect.
How this differs from four vendor apps
Vendor apps optimize for staying inside their own product. They do not hand a finished draft to a rival for review. They do not keep one activity log across providers. They do not route a cheap question away from a premium model unless you remember to switch. The cost of that fragmentation is repeated context, missed objections, and a bill that cannot explain which model produced which decision.
How this differs from an API router or a BYOK chat window
An API gateway can pick a model by price. A bring-your-own-key chat app can list several providers in one window. Symphony is built around a professional workflow: sourced research, isolated code changes, and a separate review step, with credentials and project files remaining on the Mac you control. Use those other tools when you only need a switch. Use an aggregate workspace when the job has to move from question to inspected result.
When you should not aggregate
If one vendor already covers the work, adding a coordination layer is extra cost. If you cannot connect a second model, you cannot get independent review. If every task is a one-line question, a single cheap route is enough. Symphony is for work that benefits from more than one mind — specifications, research with sources, code that should be checked, and decisions you may have to defend.
A practical place to start
Pick a real recurring job: a product decision with sources, a small code change with a review, or a spec that two models should argue over. Run it in one conversation. Inspect the evidence, the diff, and the disagreement. Expand connections only when another model adds a result you can point to.