v4

Langfuse rolled out a simplified architecture with significantly faster product performance at scale. The main table is now observations — every LLM call, tool execution, and agent step is a row you can query directly, replacing the previous trace-centric view.

Key Changes:

• Unified observations table: all inputs, outputs, and context attributes live directly on observations for faster filtering and aggregation
• Observations API v2 and Metrics API v2 designed for faster querying at scale
• Observation-level evaluations now execute in seconds
• Charts, filters, and APIs are much faster across Langfuse Cloud
• trace_id works like any other filter column (session_id, user_id, score) to group related observations

What's Faster:

• Chart loading time significantly shorter; confident loading over large time ranges
• Faster browsing of traces, users, and sessions
• Quicker filter responses in large projects
• Faster evaluation workflows

Migration Required:

• Upgrade to Python SDK v4 and JS/TS SDK v5 to avoid delays and see data in real time
• Use saved views and filters to focus on key operations across your observations table

See Fast Preview Docs for rollout details, access, and migration steps.