Upcoming architecture changes: Simplify Langfuse for Scale (v4)

[maxdeichmann]

Hi all,

On March 10, 2026, we launched Langfuse V4 as Preview on Langfuse Cloud.

This rollout is about making Langfuse much faster at scale. In v4, chart loading is significantly faster, browsing traces/users/sessions is faster, and the new Observations API v2 and Metrics API v2 perform much better on large projects. Observation-level evaluations now execute in seconds without a ClickHouse query per evaluation.

If you have questions about v4, please ask them in this discussion. We want this to be the central place for user questions on Langfuse Cloud, OSS rollout questions, migration blockers, and product feedback.

What is new in v4?

We are moving to an observation-centric data model based on a new, wide, (mostly) immutable ClickHouse table. This eliminates joins and deduplication at read-time and optimizes for the most performant ClickHouse access patterns.

Current rollout status

• v4 is currently available on Langfuse Cloud as public Beta
• You can enable it via the Preview toggle in the bottom-left of the UI
• The toggle is reversible, so you can switch back at any time
• We are still working on the migration path for OSS and self-hosted deployments

Important migration note

If you use older SDK versions, data in the new UI can be delayed by up to 10 minutes.

For real-time data in the new experience, upgrade to:

• Python SDK v4
• JS/TS SDK v5

Links

• v4 overview: https://langfuse.com/docs/v4
• changelog post: https://langfuse.com/changelog/2026-03-10-simplify-for-scale
• data model docs: https://langfuse.com/docs/observability/data-model
• Explore Observations in V4: https://langfuse.com/faq/all/explore-observations-in-v4
• Python v3 → v4 migration: https://langfuse.com/docs/observability/sdk/upgrade-path/python-v3-to-v4
• JS/TS v4 → v5 migration: https://langfuse.com/docs/observability/sdk/upgrade-path/js-v4-to-v5
• LLM-as-a-Judge migration guide: https://langfuse.com/faq/all/llm-as-a-judge-migration

We’ll keep updating this thread as the rollout evolves, especially around self-hosting and additional migrated surfaces in the product.

Looking forward to your questions and feedback.

[xstraven]

Very excited for this! We have hit some query limitations filtering large trace/session tables with many tags (had to increase the request size limit for clickhouse), so looking forward to better query performance :)

[ashishch432]

For self-hosting the underlying infrastructure components remain the same I assume?

[clemra]

Yes, correct. No changes there. This is purely a change on the data-model level, not the infra itself :)

[savitha-suresh]

Any ETA on when it will be available for self-hosting?

[maxdeichmann]

Not yet unfortunately. We are currently testing thoroughly in Langfuse Cloud and will work on a migration paths for OSS.