02.27.2026 Sessions API and CLI Support

Why Sessions Matter

LLM applications are increasingly multi-turn. Chatbots carry context across dozens of messages, coding agents iterate through plan-execute-debug loops, and RAG pipelines chain retrieval with follow-up queries. Observing individual traces tells you what happened in a single step — but to understand why a conversation went wrong, you need to see the full session. A session groups related traces from a multi-turn conversation into a single timeline. Each trace becomes a “turn” with its own start time, end time, and span tree. Session-level annotations let you attach quality scores, labels, and human feedback to the conversation as a whole rather than to isolated requests.

Sessions REST API

Four endpoints provide programmatic access to session data:

Method	Endpoint	Description
`GET`	`/v1/projects/{project_identifier}/sessions`	List sessions for a project
`GET`	`/v1/sessions/{session_identifier}`	Get a session with its traces
`POST`	`/v1/session_annotations`	Create session annotations
`GET`	`/v1/projects/{project_identifier}/session_annotations`	List session annotations

The list endpoints support cursor-based pagination and return sessions ordered by recency. The get endpoint returns the full session including every trace (turn) with timestamps.

CLI Commands

The Phoenix CLI (@arizeai/phoenix-cli@0.7.0) wraps these endpoints so you can explore sessions from your terminal.

List sessions

# Most recent sessions (default: 10)
px sessions

# Filter by project, limit results
px sessions --project my-chatbot --limit 5

# Machine-readable output
px sessions --format json --no-progress

Inspect a session

# View a session's conversation timeline
px session <session-id>

# Include quality scores and labels
px session <session-id> --include-annotations

# Export for offline analysis
px session <session-id> --file session-data.json

The pretty format renders a timeline showing each turn’s sequence number, timestamps, duration, and trace ID — useful for spotting slow turns or gaps in a conversation. JSON and raw formats return structured data suitable for piping into other tools.

Debugging with AI Coding Agents

Sessions are especially useful when paired with AI coding agents like Claude Code or Cursor. Instead of manually clicking through the Phoenix UI, you can pull session data directly into your agent’s context and ask it to diagnose issues.

# Find the slow session, then ask your agent to analyze it
px sessions --project my-chatbot --limit 5 --format raw --no-progress

# Drill into a specific session with annotations
px session <session-id> --include-annotations --format raw --no-progress

To make this available by default, add session commands to your CLAUDE.md:

## Observability

When debugging multi-turn conversations, use the Phoenix CLI to pull session data:
- `px sessions --project <name>` to find recent sessions
- `px session <id> --include-annotations` to inspect a session's
  full conversation flow, turn-by-turn timing, and quality scores
- `px session <id> --file debug.json` to save a session for deeper analysis

CLI Reference

Full command documentation

npm

Install from npm

​Why Sessions Matter

​Sessions REST API

​CLI Commands

​List sessions

​Inspect a session

​Debugging with AI Coding Agents