Langfuse Cloud: Fast Preview (v4)
Langfuse now delivers faster product performance at scale. Chart loading is much shorter, and browsing traces, users, and sessions is faster. The new Observations API v2 and Metrics API v2 query faster at scale. Observation-level evaluations now execute in seconds without a ClickHouse query per evaluation.
We will keep this page updated as we roll out additional related features and share OSS and self-hosted support updates.
Get access to the preview
In the UI, a “Preview” toggle is available in the bottom left to opt into the new experience. Not all screens have been migrated to the new data model yet.
The toggle is reversible, you can always switch back to the previous experience.
Data from SDKs langfuse-js < 5.0.0 and langfuse-python < 4.0.0 is delayed for up to 10 minutes in the new UI. Upgrade to the latest SDK versions to see your data in real time.
Migrate to the new experience
Upgrade SDKs
Upgrade to the latest major SDK versions to take advantage of the new data model and explore your data in real time:
- Python SDK: v4 (migration guide)
- JS/TS SDK: v5 (migration guide)
The key change: update_current_trace() and updateActiveTrace() are replaced by propagate_attributes(), which automatically pushes attributes like user_id, session_id, metadata, and tags to all child observations.
Optional: Migrate LLM-as-a-judge evaluations
Upgrade your LLM-as-a-judge evaluations to run at the observation level instead of the trace level for significantly faster execution. Learn more in the LLM-as-a-judge migration guide.
Optional: Adopt new observations and metrics API endpoints
The Observations API v2 and Metrics API v2 deliver significant performance improvements through the new data model:
- Selective field retrieval: Request only the field groups you need instead of full rows.
- Cursor-based pagination: Consistent performance regardless of result set size.
- Optimized querying: Built on the new immutable events table with no joins required.
See the v2 APIs announcement for migration guidance and a detailed feature comparison.
What’s faster now
Faster product performance in the UI
Chart loading time is significantly shorter. You can now confidently load charts over large time ranges. Browsing traces, users, and sessions is also much faster, and filters respond more quickly in large projects.
Faster API workflows
The new Observations API v2 and Metrics API v2 are designed for faster querying and aggregations at scale.
Faster evaluation workflows
Observation-level evaluations execute in seconds as we do not need to query ClickHouse for each evaluation anymore.
Under the hood
This preview is powered by a simplified observation-centric data model. Trace-level attributes such as user_id, session_id, and metadata now propagate automatically to observations, which helps remove expensive joins and keep the product fast at larger scale. Learn more in the data model docs and Explore Observations in V4.
OSS and self-hosting
This preview is currently available on Langfuse Cloud. We are working on the migration path for OSS deployments and will share updates here, in the changelog, and on GitHub Discussions as they become available.