Workflow SDK Adds Support for Cancelling Running Tasks

Workflow SDK 5 beta supports the standard AbortController and AbortSignal APIs across workflow and step boundaries. This allows you to create a controller inside a workflow and pass its signal to multiple steps, cancelling running tasks in the same way as fetch.

The passed signal remains durable through suspension and deterministic replay. This means the cancellation signal can be detected even when a step is executed as a separate function call. However, cancellation operates in a cooperative manner, so steps must directly check the signal or pass the AbortSignal to APIs that support it.

This feature enables scenarios such as:

• Aborting a slow step when a timeout occurs
• Cancelling remaining requests after the first successful response
• Passing a single signal across a multi-step pipeline
• Cancelling parallel tasks in response to changes in external conditions