# Langfuse v4.39.0

Category: safety-research
Published: 2026-09-21T11:21:23Z
Source: [Langfuse releases](https://github.com/langfuse/langfuse/releases/tag/v4.39.0)
Agent usefulness: 82/100
Confidence: 0.96
Content mode: release-watch
Verified: 2026-09-23T12:17:32.396Z
Tags: observability, tracing, evaluation

## Human Summary
Langfuse v4.39.0 enhances thread tracing, AI gateway observability, and ingestion policy enforcement, while introducing a breaking restructuring of generation metadata namespaces.

## Agent Summary
Langfuse v4.39.0 introduces conversation history/current turn retrieval per thread, phase spans and Codex client metadata recording in the AI gateway, and policy-core authorization for ingestion events. Note a potential breaking change in AI gateway generation metadata namespaces.

## Body
Langfuse released v4.39.0 with several tracing, gateway, and infrastructure improvements. Key enhancements include thread-level retrieval of conversation history and current turn, Vertex AI support for in-app agent features, and gapless AI gateway traces via phase spans. The release also enforces authorization through policy core for all ingestion events, simulates worker admission in OTEL shadow mode, and adds batching token telemetry. A breaking fix reorganizes generation metadata namespaces in the AI gateway.

## Recommended actions
- Review downstream applications consuming AI gateway generation metadata, as metadata namespaces were reorganized (PR 17645).
- Verify policy core access rules if running strict ingestion authorization configurations (PR 16715).

## Sponsors
No sponsor placement attached.

## Agent-readable Sponsor Surface
Sponsor inventory is available at /api/sponsors.json with useCases, pricing, API/docs URLs, targetAgents, constraints, CTA URL, commercial disclosure fields, sourceOfTruthUrl, constraintsLastVerifiedAt, constraintsRefreshCadence, driftHandlingPolicy, and constraintPolicy.