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?

[jannikmaierhoefer]

@xstraven, not sure about the exact timelines on this tbh - we will keep you updated in this thread :)

[6matt]

Very excited! Would be happy to install from scratch and test even if a migration path isn't ready yet 🙏

[magic-madrigal]

Same.

[sk0gen]

@jannikmaierhoefer Heya!
Sorry to single you out.
Are there any updates on self-hosted v4?

We plan to start using Langfuse as golang company, but seems like that v4 migration is close?

[irelandi]

Bump! Would love to know when available on the self hosted side! :)

[lssatvik-afb]

Is it alright if we upgrade our sdk to v4 and to latest langfuse version in self hosted deployment when there is no migration path? Nothing will break now and in future when migrations are available I hope?

[xstraven]

@lssatvik-afb I asked the same question in the community hour yesterday and my understanding is that the v4 Python SDK points some methods to new v2 endpoints that are not part of the latest self-hosting versions. We are keeping python langfuse <= 3.x for now while the new data schema is not rolled out for self-hosted.

cc @Lotte-Verheyden

[lssatvik-afb]

@xstraven Thanks for sharing this!

[hassiebp]

For self-hosters, you may upgrade to the latest SDK versions with two caveats:

1. client.api.observations and client.api.metrics are now pointing to new endpoints that are not yet supported on the legacy self-hosted images. Use client.api.legacy.* instead
2. Trace input and output must be set manually if you depart from the default input output of the root span. https://langfuse.com/docs/observability/sdk/instrumentation#trace-inputoutput-behavior

[jkaushal]

Very Excited to be exploring this.

Probabaly some one has already answered, but I want a neat way to associate an Eval List with specific Prompt/Prompt Groups. Is there a native langfuse way to do this?

[ashgold]

When developing V4, I would like to see dashboard query speed optimized using Incremental Materialized View in ClickHouse. Currently, V3 reads all raw data, so query speed slows down significantly as the number of rows in a table increases.

[AlexanderLB98]

Hey! I was just checking langfuse and Im planning to implement it in my project. With no prior experience with v2/v3, would it be recomended to start directly with v4 or just start with v3 until there is a stable release?