Background tasks let a tool run while the agent keeps working, instead of blocking the loop until it finishes. This is a Strands Harness SDK capability, exposed through Strands harness’s `background_tasks` / `backgroundTasks` option.

## What runs in the background by default

The built-in `generalist` [delegate](/docs/user-guide/harness/configure/subagents/index.md) always runs in the background, so the main agent can continue while the delegate works through its subtask. By default the model may also choose background execution for any other compatible tool; the invocation waits for the result and continues with it.

## Tune or disable it

`backgroundTasks` accepts a boolean or a policy object. Pass `false` to disable background tasks, or a policy to control which tools may run in the background, along with concurrency, completion, and timeouts. With a policy, the `generalist` still runs in the background: Strands harness forces it there and merges that into your policy.

```typescript
import { createHarness } from '@strands-agents/harness'

// Disable background tasks:
const noBackground = await createHarness({ backgroundTasks: false })

// Or supply a policy for the other tools:
const scoped = await createHarness({
  backgroundTasks: { agentic: ['long_running_report'] },
})
```

The default policy is equivalent to `{ agentic: ['*'] }`: the model may run any compatible tool in the background.

## The CLI

The Strands harness CLI runs on the TypeScript library, so the `generalist` runs in the background there too. The CLI does not expose a flag to change the background-tasks policy; use the library when you need to tune it.

For the full option list, see the [configuration reference](/docs/user-guide/harness/reference/configuration/index.md).

## Implementation

### TypeScript

- [harness-sdk/harness-ts/src/agent.ts](https://github.com/strands-agents/harness-sdk/blob/main/harness-ts/src/agent.ts)