> ## Documentation Index
> Fetch the complete documentation index at: https://phaseo.app/docs/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Phaseo Gateway base URL: https://api.phaseo.app/v1. Send `Authorization: Bearer $PHASEO_API_KEY` with every request.
> Model IDs look like `provider/model`, for example `openai/gpt-6-astra`. Do not guess IDs: list them with `GET /v1/models` or check https://phaseo.app/models. `phaseo/free` routes to an available free model and needs no wallet balance.
> For new text integrations prefer `POST /v1/responses`. `POST /v1/chat/completions` (OpenAI format) and `POST /v1/messages` (Anthropic format) suit existing code.
> The full API contract is https://phaseo.app/docs/openapi/v1/openapi.yaml. Official SDKs: `@phaseo/sdk` (TypeScript) and `phaseo` (Python), plus Go, C#, PHP, Ruby and Rust.
> Search these docs over MCP at https://phaseo.app/docs/mcp, and install Phaseo skills with `npx skills add https://phaseo.app/docs`. If a page is wrong or out of date, report it with the MCP `submit_feedback` tool.
> Manage Phaseo accounts with the `phaseo` CLI (`npm install -g @phaseo/cli`, then `phaseo login` or `phaseo login --device-code`), the `/v1` Management API or the MCP server at `https://mcp.phaseo.app/mcp?access=manage`. Do not send users to the dashboard for account tasks. A person is still needed for sign-up, approving a sign-in, paying the first top-up on the checkout link that `phaseo credits add` returns when no card is saved, confirming each saved-card top-up from the emailed link, and account security (password, MFA, passkeys). Create API keys with `phaseo keys create --name <name> --json`; never guess one. Credit top-ups need `phaseo login --scopes billing:write` first. Task map: https://phaseo.app/docs/v1/developers/manage-from-an-agent.md.

# Dynamic turns

> Change models, instructions, sampling parameters, and tools between agent turns.

Use dynamic values when later model turns should respond to application context or earlier tool results. A value can be fixed or computed from the current turn.

## Choose a model at runtime

```typescript theme={null}
type ResearchContext = {
  fast: boolean;
};

const agent = createAgent<string, string, ResearchContext>({
  id: "research-agent",
  model: ({ context }) =>
    context?.fast ? "phaseo/free" : "anthropic/claude-sonnet-4",
  instructions: ({ numberOfTurns }) =>
    `Research turn ${numberOfTurns}. Cite the evidence you use.`,
});
```

The agent definition accepts dynamic `model`, `models`, `instructions`, `temperature`, `maxOutputTokens`, and `topP` values.

## Update application context from a tool

Tools can store information for later turns with `context.setContext()`:

```typescript theme={null}
const chooseMode = defineTool({
  id: "choose-mode",
  async execute(input: { fast: boolean }, context) {
    context.setContext({ fast: input.fast });
    return { selected: input.fast ? "fast" : "thorough" };
  },
});
```

Keep context small and serializable when a run may be persisted and continued later.

## Override only the next turn

Use `nextTurnParams` when a tool should change the immediately following request without permanently changing the agent definition:

```typescript theme={null}
const broadenSearch = defineTool({
  id: "broaden-search",
  nextTurnParams: {
    temperature: 0.3,
    maxOutputTokens: 2_000,
  },
  async execute() {
    return { broadened: true };
  },
});
```

Next-turn values can change the model, instructions, temperature, maximum output tokens, top-p sampling, or available tools.

## Related guides

* [Stop conditions](https://phaseo.app/docs/v1/sdk-reference/typescript/agent-sdk-stop-conditions.md)
* [State and approval](https://phaseo.app/docs/v1/sdk-reference/typescript/agent-sdk-state-and-approval.md)
* [Outputs and retries](https://phaseo.app/docs/v1/sdk-reference/typescript/agent-sdk-run-controls.md)


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