How do I check whether I am on Langfuse v4?
Langfuse Cloud
- Organizations created on or after April 14, 2026 run Langfuse v4 and do not show a toggle.
- Organizations created before that date show a Langfuse v4 preview toggle in the bottom-left corner of the UI until the v4 cutover. When the toggle is on, you see the v4 experience.
- The Migration Assistant sidebar panel and the Migration status page list the remaining actions for your projects.
Self-hosted Langfuse
Two things decide whether your instance is on v4:
- Server version.
GET /api/public/healthreturns the running version in theversionfield, for example"version": "4.75.0". The version is also shown in the UI sidebar. Versions starting with4.are Langfuse v4. - Write mode. A v4 server can still run in a migration mode.
LANGFUSE_MIGRATION_V4_WRITE_MODEcontrols it:
LANGFUSE_MIGRATION_V4_WRITE_MODE | Meaning |
|---|---|
events_only (default) | Fully on v4. All users see the v4 experience. |
dual | Migration in progress. Users can switch the v4 preview on and off, unless LANGFUSE_MIGRATION_V4_ALLOW_PREVIEW_OPT_IN=false. |
legacy | v3 behavior on a v4 server. |
For the migration steps, see Migrate Langfuse v3 to v4. To prepare a project, see Make your project ready for the upgrade to Langfuse v4.
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