# Asynchronous Activity completion - Go SDK

> Asynchronous Activity Completion lets the Activity Function return without finishing Activity Execution. Use Task Tokens and Temporal Client to complete the Activity externally.

[Asynchronous Activity Completion](/activity-execution#asynchronous-activity-completion) enables the Activity Function to return without the Activity Execution completing.

There are three steps to follow:

1. The Activity provides the external system with identifying information needed to complete the Activity Execution.
   Identifying information can be a [Task Token](/activity-execution#task-token), or a combination of Namespace, Workflow Id, and Activity Id.
2. The Activity Function completes in a way that identifies it as waiting to be completed by an external system.
3. The Temporal Client is used to Heartbeat and complete the Activity.

**Step 1: Provide the external system with a Task Token to complete the Activity Execution.**
   To do this, use the `GetInfo()` API from the `go.temporal.io/sdk/activity` package.

```go
// Retrieve the Activity information needed to asynchronously complete the Activity.
activityInfo := activity.GetInfo(ctx)
taskToken := activityInfo.TaskToken
// Send the taskToken to the external service that will complete the Activity.
```

**Step 2: Return an `activity.ErrResultPending` error to indicate that the Activity is completing asynchronously.**

```go
return "", activity.ErrResultPending
```

**Step 3: Use the Temporal Client to complete the Activity using the Task Token.**

```go
// Instantiate a Temporal service client.
// The same client can be used to complete or fail any number of Activities.
// The client is a heavyweight object that should be created once per process.
temporalClient, err := client.Dial(client.Options{})

// Complete the Activity.
temporalClient.CompleteActivity(context.Background(), taskToken, result, nil)
```

The following are the parameters of the `CompleteActivity` function:

- `taskToken`: The value of the binary `TaskToken` field of the `ActivityInfo` struct retrieved inside
  the Activity.
- `result`: The return value to record for the Activity. The type of this value must match the type
  of the return value declared by the Activity function.
- `err`: The error code to return if the Activity terminates with an error.

If `err` is not null, the value of the `result` field is ignored.

To fail the Activity, you would do the following:

```go
// Fail the Activity.
client.CompleteActivity(context.Background(), taskToken, nil, err)
```