Both trace agents, run experiments and score production traffic. Galileo, now Splunk Agent Observability, adds runtime guardrails on tool inputs and outputs and fits Splunk estates; LangSmith is the self-serve choice for teams on LangChain or LangGraph. Your existing stack usually decides this one.[3][4]
Galileo is now sold as Splunk Agent Observability after Cisco's acquisition completed in May 2026. It pairs evaluation with Agent Control, which can block harmful tool inputs and outputs during a run. LangSmith is LangChain's platform: a free single-seat tier, per-seat paid plans, prompt versioning and a model-call gateway in beta. Splunk teams lean Galileo; LangChain teams lean LangSmith.
| Decision factor | Galileo | LangSmith |
|---|---|---|
| Ownership | Acquired by Cisco (completed May 2026); sold as Splunk Agent Observability since 7 August 2026 | LangChain, independent; $125M Series B in October 2025 |
| Runtime guardrails | Yes: Agent Control checks LLM and tool inputs and outputs during execution | Partial: LLM Gateway (beta) applies spend caps, model access and redaction to model calls |
| Evaluators | Preset and custom LLM judges, Luna-2 small models, Python code metrics (not in the Splunk-hosted edition) | LLM-as-judge, pairwise and code evaluators, offline and online |
| Prompt tooling | Prompts and playground; version control not documented | Prompt Hub with commit-based versioning, tags and a playground |
| Self-hosting | On-premises, including air-gapped (commercial) | Enterprise add-on, or BYOC data plane |
| Free tier | None listed for Agent Observability | Developer: 1 seat, 5k base traces a month |
| Paid pricing | From $100 a month per 1.2 million spans a year, billed annually | Plus: $39 per seat a month, 10k base traces |
| Capability | Galileo | LangSmith | Prefactor |
|---|---|---|---|
| Observe | |||
| LLM call tracing | ✓ | ✓ | ✓ |
| Multi-step agent tracing (tool calls, nested spans) | ✓ | ✓ | ✓ |
| Cost tracking | ✓ | ✓ | ✓ |
| OpenTelemetry support | ✓ | ✓ | ✓ |
| Evaluate | |||
| Offline evals (datasets, experiments) | ✓ | ✓ | ✓ |
| Online evals on production traffic | ✓ | ✓ | ✓ |
| LLM-as-a-judge scoring | ✓ | ✓ | ✓ |
| Code-based evaluators | ✓ | ✓ | ✓ |
| Human review and annotation | ✓ | ✓ | ✓ |
| Prompt versioning and playground | Partial | ✓ | — |
| Act on findings | |||
| Runtime controls on live agent actions | ✓ | Partial | ✓ |
| Gateway or proxy in the request path | — | — | — |
| Licence and deployment | |||
| Open source | Partial | Partial | Partial |
| Self-hosting | ✓ | ✓ | Partial |
Cisco completed its acquisition of Galileo in May 2026, and since 7 August 2026 the product is sold as Splunk Agent Observability inside Splunk Observability Cloud. Customers who joined before that date still use Galileo's documentation; later customers use Splunk's. The old pricing page redirects to Splunk, which lists paid pricing billed annually and no free tier for this product.
That makes the decision easier for some teams. If you already send infrastructure and application telemetry to Splunk, agent evaluation in the same place is a strong reason to choose it. If you do not use Splunk, expect a sales-led purchase rather than a self-serve trial.
Galileo's Agent Control evaluates model and tool inputs and outputs while an agent runs and can block prompt injection, personal data leaks and harmful content using centrally set rules, without changes to agent code. It replaced the older Protect product in June 2026, and its core was released as open source under Apache-2.0 in March 2026.
LangSmith's LLM Gateway, in public beta since 30 July 2026, sits in the model-call path and can cap spend, restrict which models are used and redact personal data or secrets. It covers model calls only; LangChain describes gateways for tool calls and MCP as planned. If you need checks on what an agent does with its tools, Galileo covers more of that today.
LangSmith's strength is the loop from trace to dataset to experiment, with prompt versioning and a playground in the same place, and the deepest integration with LangChain, LangGraph and Deep Agents. Its Engine, in public beta since May 2026, reads production traces and drafts proposed fixes.
Galileo offers experiments, multi-turn evaluation and Luna-2 small models as lower-cost judges. One limit to check: the Splunk-hosted edition supports five preset Luna evaluators and no custom code evaluators, which are available on-premises only.
LangSmith is the natural fit if you build on LangChain, LangGraph or Deep Agents, but it is not limited to them: it also documents integrations for the OpenAI Agents SDK, Claude Agent SDK, CrewAI, AutoGen, Google ADK and Mastra, and it ingests OpenTelemetry traces, mapping OpenInference and OpenLLMetry attributes.
Galileo documents native integrations for the OpenAI Agents SDK, LangGraph, CrewAI, Google ADK, Strands, Microsoft Agent Framework and multi-agent tracing over A2A, and accepts OpenTelemetry traces, with OpenInference instrumentors for Python only. Either can trace a framework-agnostic agent.
The team question is about buying, not tooling. LangSmith starts free for one person and adds seats as the team grows, which suits a small team proving value. Splunk Agent Observability is billed annually on span volume and bought through Splunk, which suits an organisation that already has that relationship.
As of 20 October 2026, LangSmith's Developer tier is free for one seat and 5k base traces a month, and Plus is $39 per seat a month with 10k base traces; the overage rate per trace is not published. Splunk Agent Observability starts at $100 a month per 1.2 million spans a year, billed annually, with a Luna token allowance. Per-seat pricing grows with your team; span-based pricing grows with your traffic.
We sell the layer this section describes. Read it with that in mind.
Stated plainly, since Prefactor publishes this page: Prefactor is an agent evaluation platform that scores each step of a run and acts on what it finds through runtime policies on tool calls and data access, approval holds for risky actions, and a kill switch. Of these two, Galileo's Agent Control is the closest to that; LangSmith's gateway covers model calls. Prefactor is self-serve with a free tier and is not tied to Splunk or LangChain, but it has no prompt playground. See the full comparison of 15 platforms.
Reviewed against public product and documentation pages on October 20, 2026. If a vendor has changed a feature, product name, or positioning since then, send a correction and we will update it. Numbered source links in the page body point to the ordered sources below.
Prefactor scores each step of every agent run and can hold or stop an action when a score says it should not happen. Start on the free tier: 5,000 spans a month, no credit card required.
Prefactor helps teams observe, evaluate, and improve their AI agents in production, across every framework and provider.