Sessions
A Session groups multiple traces that belong to the same logical interaction under a shared session_id. Sessions let you replay entire conversations end-to-end, analyze them as a unit, annotate outcomes, and manage related traces together. You can explore sessions for filtering, cohort analysis, debugging, and evaluation at the conversation level.

In a customer support scenario, each time a user sends a message and receives a response, that exchange generates its own trace. When the user follows up with clarifying questions or the conversation escalates to a different topic, each of those exchanges creates additional traces. The session ties all of these traces together under a single identifier, capturing the full support ticket from the customer's first message to resolution.
The sessionId can be any US-ASCII character string less than 200 characters, if it exceeds it will be dropped.
Why Sessions Matter
LLM-powered applications often span multiple requests. A single user conversation might generate dozens of traces across different turns. Without sessions, these traces appear as disconnected events. Sessions provide the logical grouping needed to:
Replay entire conversations from start to finish
Analyze multi-turn interactions as a unit
Annotate outcomes at the conversation level
Compare session-level metrics across cohorts
Debug issues that only appear across multiple turns
Click on any session to open the detail view, which displays the complete list of traces in chronological order, session-level scores and annotations, total duration, cost, token usage, and user information.
Creating a Session
To create a session, assign the same session_id to multiple traces. There is no separate "create session" call — the session is automatically created the first time a trace references a given session_id.
Use update_current_trace() inside a decorated function to set the session and user:
If your traces have multiple nested observations that all need the same session_id and user_id, use propagate_attributes instead. For details and parameters, see Updating Traces.
Translating Content
Click the translate icon in the session detail header to enable translation mode. Content is not translated all at once, each trace is translated individually when expanded. Click the icon again to revert all content to the original language.

Properties of a Session
Id
Unique session identifier
Created At
Timestamp when the first trace was added to the session
Duration
Total time span from first to last trace in the session
Environment
Deployment context like production, staging, or development
User IDs
End-users associated with traces in this session
Traces
Number of traces grouped under this session
Input/Output Cost
Cost of input/output tokens across all traces in the session
Total Cost
Accumulated cost (input + output) across all traces
Input/Output tokens
Number of input/output tokens consumed across all traces
Total Tokens
Total token count (input + output) across all traces
Usage
Breakdown of token consumption by model
Trace Tags
Aggregated tags from all traces in the session.
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