# Langfuse v4.64.0

Category: safety-research
Published: 2026-10-19T17:34:15Z
Source: [Langfuse releases](https://github.com/langfuse/langfuse/releases/tag/v4.64.0)
Agent usefulness: 94/100
Confidence: 0.96
Content mode: release-watch
Verified: 2026-10-19T18:17:51.682Z
Tags: observability, tracing, evaluation

## Human Summary
Langfuse released v4.64.0, renaming Langfuse Assistant to Halo, defaulting project API key permissions, exposing legacy API deprecations to code agents, and introducing request admission control by memory budget in the AI Gateway.

## Agent Summary
Langfuse v4.64.0 update highlights: renamed Assistant to Halo, enabled project API key permissions by default, surfaced legacy API deprecation notices to code agents, enforced memory-budget-based request admission in the AI Gateway, and restricted public API project keys from accessing paths of other projects.

## Body
Langfuse v4.64.0 introduces several new features, fixes, and chore updates across its tracing, API, and gateway components. Notable additions include renaming the Langfuse Assistant to Halo, defaulting project API key permissions, making legacy API deprecation notices visible to code agents, admitting AI Gateway requests by memory budget only, and adding run cost tracking to topics. Fixes include enforcing project scoping on API keys (rejecting keys when paths target other projects), dropping non-numeric cost details on direct OpenTelemetry events, preventing soft-deleted rows from appearing in event reads, and masking Halo questionnaire content from session replays.

## Recommended actions
- Verify that API keys match the specific project path they target, as mismatched paths are now refused by the public API.
- Review API interactions if using code agents, as legacy API deprecation notices are now explicitly surfaced to them.
- Note the renaming of Langfuse Assistant to Halo across integrations and documentation.

## 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.