> ## Documentation Index
> Fetch the complete documentation index at: https://docs.alpha.isaree.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Primary Agent
> Configure the Primary Agent in Isa — pick its model (on-device or cloud) and edit the system prompt that shapes its behavior.
The Primary Agent is the agent you talk to in [Patient Chat](/isa/patient-chat) — every Patient Chat is a conversation between you and the Primary Agent, *about* the patient. The Primary Agent interprets what you say, calls [Agents](/concepts/agent) and [MCP Servers](/concepts/mcp-servers), and produces the response. You have to pick a Primary Agent before you can open a Patient Chat.
The Primary Agent does not operate in [Workspace](/isa/workspace) — Workspace lets you chat directly with an Agent.
This page covers two things: the model behind the Primary Agent, and its system prompt.
## Open the Primary Agent Model picker
Open [Settings](/isa/settings) in Isa, then open **Primary Agent Model**. The picker has three parts:
* **IN USE** at the top — the active variant, with size, capabilities, and where it runs (on-device or cloud).
* **Thinking Mode** toggle — for models that support step-by-step reasoning.
* **Model Families** — grouped by maker (Qwen 3.5, Liquid 2.5, Gemma 3, Llama 3.2, Qwen 3) for on-device, plus OpenAI and Aki.io for cloud. A green dot marks the family the active variant comes from.
## Pick on-device or cloud
The first decision is where the model runs:
* **On-device** — the model runs on your iPhone, iPad, or Mac. What the Primary Agent processes — the chat, transcripts, OCR text — never leaves your device. Restricted to models small enough to fit in [RAM](/concepts/ram-device-memory).
* **Cloud** — the model runs via OpenAI or Aki.io. The conversation leaves your device when it does. You bring your own API key.
See [On-device vs. cloud](/concepts/on-device-vs-cloud) for the deeper trade-off, and [Data and privacy](/get-started/data-and-privacy) for what data flows where.
The Primary Agent and any Agent you invoke share your device's RAM. Pick a Primary Agent small enough to leave room for the Agents you actually use.
## Pick an on-device Primary Agent
The on-device families are pre-vetted lists of open-weight models that run on Apple hardware. Open a family to see its variants. Each variant lists size in GB, capabilities (Vision, Thinking), and the iPhone it's tested on.
Solid defaults for clinical use:
* `Qwen 3.5 (4B)` — careful and thorough for longer histories, nuanced summaries, and busy documents. Best on iPhone 16 Pro / 17 Pro.
* `Qwen 3.5 (2B)` — everyday default for visit summaries, referrals, and lab-photo extraction. Best on iPhone 15 Pro / 16 / 17.
* `LFM 2.5 Thinking (1.2B)` (Liquid 2.5 family) — small reasoning model for tool-heavy workflows when you need to leave room for Agents.
**Download** a variant to install it. Once it's installed, select it to make it active. Variants you've downloaded show **Delete** instead.
For deeper sizing guidance, see [Choose a model](/guides/choose-a-model).
## Pick a cloud Primary Agent
OpenAI and Aki.io are families inside the picker. Open one and you'll see:
* **API key** at the top — paste your key and save it. The key stays on your device. Once saved, the family shows an "API key saved" badge with the last four characters.
* **Variants** below — pick one to make it active. There's nothing to download.
Two cloud providers:
* **OpenAI** — OpenAI's proprietary models.
* **Aki.io** — hosts open-weight models (Llama 3.3 70B, Qwen 3.6 35B, Gemma 4 26B, GPT-OSS 120B, MiniMax M2.5 230B) on EU infrastructure and uses the same API format as OpenAI. Cheaper than OpenAI.
## Switch between models
To change the active Primary Agent, open the picker and pick any other variant — on-device or cloud, in any family. The new variant becomes active immediately and the **IN USE** panel updates. API keys and downloaded models stay in place, so switching back is a single tap.
## Turn on Thinking Mode
The **Thinking Mode** toggle at the top of the picker lets compatible models reason step-by-step before answering. Models that support it carry a **Thinking** badge.
Thinking Mode improves accuracy on complex questions but slows responses. It can also reduce reliability when the Primary Agent is calling [MCP Servers](/concepts/mcp-servers) or other Agents — turn it off if you're running tool-heavy workflows and seeing flaky behavior.
A handful of variants (like `Qwen 3 Thinking (4B)`) are always-thinking regardless of the toggle.
## Edit the system prompt
The [system prompt](/guides/create-a-system-prompt) tells the Primary Agent how to behave in Patient Chat — its tone, and what it should and shouldn't do. Open it from Settings → **System Prompt**.
An [Agent's](/concepts/agent) system prompt and the Primary Agent's system prompt do different jobs. An Agent's prompt is narrow — it describes the one task that Agent is built for (summarise a visit, extract labs, draft a referral). The Primary Agent's prompt is broader — it sets the tone, ground rules, and response style across every Patient Chat.
Changing the system prompt changes how the Primary Agent behaves in every Patient Chat conversation. Edit carefully — if you're unsure, ask in [Discord](https://discord.gg/2R6VvHZpdn).
## Know what else this affects
The model you pick has consequences elsewhere in Isa:
* **Where the Primary Agent's data goes.** An on-device variant keeps the chat, [OCR](/concepts/ocr) text, and Scribe transcripts the Primary Agent sees on the device. A cloud variant sends them to the provider. This setting only governs the Primary Agent — cloud Scribe Agents and external MCP Servers still send their own data off-device regardless of which Primary Agent you pick.
* **Camera is VLM-only.** The **Camera** button in Patient Chat only appears when the active variant is a [VLM](/concepts/llms-vlms) (carries the **Vision** badge). OCR via **Scan Doc** works either way.
## Next
Size the Primary Agent for the device — parameter count, [quantization](/concepts/quantization), RAM headroom.
What stays on-device versus what leaves it.
The main surface where the Primary Agent does its work.