Langfuse v4 is live: faster at scale, with more ways to search, monitor, and evaluate

Max Deichmann

Query and evaluate every agent step directly, with initial table loads in milliseconds and at least 10x faster dashboards for large projects.

Langfuse v4 is live on Langfuse Cloud and generally available for self-hosted deployments. It makes it faster to debug, evaluate, and monitor complex LLM applications by letting you work with every LLM call, tool execution, and agent step directly. Initial table loads over large datasets drop from seconds to milliseconds, and dashboards over longer time ranges load at least 10x faster in large projects.

Langfuse Cloud becomes v4-only on November 16, 2026 (2026-11-16). Most projects need no migration. If the Migration Assistant shows actions for your project, complete them before this date.

What we shipped in Langfuse v4

Langfuse v4 is much faster and also ships new ways to search, monitor, evaluate, and query your application data. Check them out:

• Monitors: Watch cost, quality, and latency thresholds and notify teams through Slack, webhooks, or GitHub Actions.
• Code evaluators: Run deterministic Python or TypeScript checks on live observations and experiments.
• Filter search bar: Combine typed filters, metadata, and scores in one shareable query.
• Full-text search: Find words and phrases across observation inputs, outputs, and metadata.
• Pulse: Plot count, cost, or latency above the Observations table and select a spike to inspect its operations.
• Langfuse Assistant: Ask questions about traces, observations, sessions, and metrics in plain language.
• Observations API v2: Retrieve selected observation fields with cursor-based pagination.
• Metrics API v2: Aggregate cost, tokens, volume, latency, and scores across observations.

Upgrade Langfuse Cloud projects

Langfuse Cloud deprecates v3 endpoints and features on November 16, 2026 (2026-11-16). Please complete any migration requirements for your projects before this date.

New projects already use v4 and need no migration.

For existing projects, organization owners can open the Migration Assistant sidebar and the Migration status page to see if any actions are required:

We will email project owners and admins a summary of the actions required for their projects. Complete those actions by November 16, 2026 (2026-11-16).

Follow the upgrade guide for more details.

Upgrade self-hosted Langfuse instance

Langfuse v4 is generally available for self-hosted deployments. There is no forced cutover date, and Langfuse v3 will receive security patches through January 2027.

Follow the self-hosted v3 to v4 migration guide to review the infrastructure requirements and plan your upgrade.

Technical background: V4 does less work for the same query

• Queries scan less data. One denormalized observations table replaces read-time joins between traces and observations.
• Ingestion writes less data. Each completed observation is written once.
• Immutable data creates room to optimize. Append-only observations give us the architectural freedom to introduce optimizations such as materialized views in the future.

Older SDKs sent updates to both traces and observations, which we stored in separate tables. Before ClickHouse could return a result, it had to join those tables and deduplicate the updates. This was slow at scale.

The Langfuse Python SDK 4.7.0 or later and JS/TS SDK 5.4.0 or later add trace-level attributes such as user_id and session_id to every observation before it is ingested into Langfuse. Each observation is written to a new immutable, append-only table. The same query now needs neither a join nor deduplication, which makes it much faster.

Questions

Ask rollout and migration questions via the in-app support form or on the v4 GitHub Discussion post.

You can also join a live Q&A with the Langfuse engineering team. Bring migration questions or your actual setup:

Step-by-step upgrade guide Versions & Compatibility Working with observations Ask questions on Langfuse v4