What are the intended semantics of BaseEvent.timestamp?

[ushiboy]

Hello,

I have a question regarding the intended semantics of BaseEvent.timestamp.

While integrating Google ADK with AG-UI, I started looking into how BaseEvent.timestamp is intended to be used.

From what I found:

• BaseEvent defines an optional timestamp field.
• However, none of the integrations under this repository appear to populate it (ADK, LangGraph, CrewAI, Langroid, AWS Strands, Watsonx, Claude Agent SDK, etc.).
• This consistent behavior makes me wonder whether this is an intentional design decision rather than an implementation oversight.

Questions

1. What is BaseEvent.timestamp intended to represent?

   • The timestamp of the original source framework event?
   • The time when the AG-UI event is emitted?
   • Or is it intentionally left unused by integrations?

2. Is leaving timestamp unset the intended behavior for integrations?

I'd appreciate any clarification on the intended design.

Thank you!

[barry166]

From the current SDK docs/types, I would treat timestamp as an optional AG-UI event creation time, not as a required source-framework timestamp.

The proto and Python model both make it optional, and the Go SDK docs describe it as Unix milliseconds for when the event was created. So integrations leaving it unset is valid. If an adapter does populate it, the least surprising value is the time the adapter emits/translates the AG-UI event; if you need the original framework event time, keep that in rawEvent or adapter-specific metadata.

I also would not use timestamp as the ordering contract. Stream order plus runId/messageId/tool-call ids should remain the source of ordering.