# Nexus Standalone Activity

> For the complete documentation index, see [llms.txt](https://docs.temporal.io/llms.txt).
> Any documentation page is available as raw Markdown by appending `.md` to its URL.

> Back a Nexus Operation with a Standalone Activity when the work is a single durable step, with no Workflow wrapped around it.

> **Pre-release** — Go, Java, Python, TypeScript, .NET
> APIs are experimental and may be subject to backwards-incompatible changes.

> **📝 Note:**
> Not the same as a Standalone Nexus Operation
>
> The two names are close and describe opposite ends of the call.
> A [Standalone Nexus Operation](/standalone-nexus-operation) is about the **caller**: a Client starts an Operation directly, with no caller Workflow around it.
> A Nexus Standalone Activity is about the **handler**: an Operation is backed by a single Activity, with no Workflow behind it.
> They are independent choices, and either can be used without the other.
>

An Activity-backed [Nexus Operation](/nexus/operations) runs a [Standalone Activity](/standalone-activity) and completes when that Activity returns.
Use it when the work behind an Operation is one durable step rather than a process: calling an external API, running a computation, writing to another system.

Two things combine to make this happen.
The [Activity](/activities) supplies durability — retries on the policy you set, timeouts you control, and a record of every attempt.
The Operation supplies a typed contract and a [Namespace](/namespaces) boundary, so another team can call it without sharing your code, your deployment, or write access to your Namespace.

Because the Activity carries the durability, no Workflow is needed behind the Operation.
A Workflow wrapping a single Activity costs two [Billable Actions](/cloud/actions-usage#actions-in-workflows) in Temporal Cloud — one to start the Workflow, one to start the Activity — where a Standalone Activity costs one.
Retries and heartbeats are billed the same way in either shape.

## Required options

Starting an Activity this way needs values a Workflow-called Activity does not, because there is no parent Workflow to supply them:

- **An Activity Id**, unique within the Namespace. Deriving it from the Nexus request Id makes the start idempotent, so a retried request targets the same Activity Execution instead of sending a second notification or charge.
- **A timeout.** At least one of start-to-close or schedule-to-close.

The Task Queue is optional and defaults to the one the Operation is running on. Set it explicitly to run the Activity on its own Worker fleet.

## Cancellation

An Activity is not interrupted by a cancellation request the way a Workflow is.
The Worker only learns about it on the next Heartbeat, so an Activity that never Heartbeats runs until it completes or times out.
Nothing here is Nexus-specific — see [Activity Cancellation](/activity-execution#cancellation).

Back an Operation with a **Workflow** instead when the work has more than one step, needs to wait for something, needs to receive [messages](/sending-messages), or needs durable intermediate state.