It seems likely that Phoenix's Prompt Playground now supports client-side run cancellation, so you can detect when a user clicks "stop" and mark a prompt as cancelled on the client. However, server-side cancellation (actually halting the backend LLM run) is not yet implemented, so the backend may continue processing even after the UI shows cancellation. There is no explicit mention in the data sources of a built-in way to annotate or propagate cancellation events (like "user clicked stop") into traces or sessions metadata, nor is there documentation on surfacing this in the session thread UI鈥攃urrently, cancelled runs may just show as "undefined" in the UI while the backend continues working.
If you want to expand this to include more detailed cancellation context (e.g., "user clicked stop"), you would likely need to implement custom metadata or annotations yourself, as there is no out-of-the-box support for this in Phoenix at this time. Would you like more detail on how to add custom annotations or metadata to traces or sessions to track cancellation events?
Sources:
- <https://github.com/Arize-ai/phoenix/pull/5566|feat: Add cancel button to playground runs>
