Specialist Models
Specialists are non-main models that a multi-model party exposes as tools to the main agent.
A Specialist is any model in a multi-model party other than the Main Agent and Default Sub-Agent. Specialists exist because real coding work occasionally needs something the main model is bad at — image understanding, OCR, segmentation, image generation, TTS, audio transcription, time-series forecasting — and dragging the main model through those tasks is wasteful.
How specialists become tools
When a party deploys, every specialist is registered with the Main Agent as a tool. The tool description comes from the catalog entry's structured description, which tells the Main Agent what the specialist is good at and when to call it.
The Main Agent then calls the specialist exactly the way it would call any other tool. The Bridge intercepts the call, forwards it to the specialist (with whatever payload is appropriate for the specialist's modality), and folds the response back into the conversation.
Custom instructions per specialist
When you compose a party, every specialist gets an optional instruction string. The instruction tells the Main Agent how to use that specialist — for example, "use this specialist for OCR on scanned PDFs, not for OCR on screenshots". Custom instructions are the cheapest way to make a generic capability behave well in your specific workflow.
Cost & latency
Specialists are usually smaller and cheaper than the Main Agent. Routing routine work to a specialist instead of the Main Agent saves both tokens and time. The Party Builder's plan view shows the expected cost shape so you can predict the savings before deploying.
Specialists that aren't LLMs
Many specialists are not LLMs at all — image generators, segmenters, TTS, audio generators, mesh recovery, UI grounding, time-series forecasters. Each surfaces as a purpose-specific tool matched to its modality, so the Main Agent invokes the right tool for the right kind of work.