Arthur vs Lakera
Both are guardrails & safety tools. Here is how they actually differ on price, billing model and deployment.
Arthur
Open-sourced its real-time evaluation engine and, unusually for this segment, publishes actual prices. Free tier has unlimited seats; Premium is $60/mo. The meter is use cases rather than volume, which is worth understanding.
Lakera
The best-known prompt injection defence API, acquired by Check Point in September 2025 for a reported $300M. Still developed by the original Zurich team, but sales now run through Check Point enterprise procurement.
| Arthur | Lakera | |
|---|---|---|
| Category | Guardrails & Safety | Guardrails & Safety |
| Our rating | 4/5 | 4/5 |
| Starting price | $60/mo | Not published |
| Billing meter | use-case | No usage metering |
| Free plan | Yes | Yes |
| Free self-hosting | Yes, free | No or paid tier only |
| Best for | Teams that want open-source guardrails running inside their own stack with the option of an inexpensive managed tier, and who value published pricing and unlimited seats. | Teams that want managed, low-latency prompt injection defence with enterprise support and are comfortable with a proprietary API and an enterprise sales process. |
Our verdict on Arthur
Arthur is the most transparent vendor in a segment that has almost none. It publishes actual prices - Free at zero with unlimited seats and four use cases, Premium at $60 a month for a hundred - while Lakera, Fiddler, HiddenLayer, CalypsoAI and Prompt Security all require a sales conversation before you can learn anything about cost. It also open-sourced the Arthur Engine, a real-time evaluation and guardrails service covering PII and sensitive data leakage, hallucination, prompt injection and toxicity, which runs locally inside your own stack rather than shipping prompts to a third party. That combination of published pricing, permissive licensing and in-environment execution is genuinely rare here. Two things to understand. The meter is use cases rather than requests or volume, and what constitutes a use case is not obvious from the pricing page, so establish that before budgeting. And Arthur Shield, the enterprise LLM firewall, is a separate product with custom pricing, so the transparent prices do not cover the whole guardrails story.
Full Arthur review →Our verdict on Lakera
Lakera is the strongest managed prompt injection defence available and the acquisition has not obviously damaged it. Check Point acquired the company in September 2025 in a deal reported around $300 million, taking Lakera Guard, Lakera Red and the Gandalf dataset into its AI security platform, and basing its Global Center of Excellence for AI Security on the Zurich team. That team still maintains the detection models, which is the outcome you want from an acquisition and is notably better than what happened to Helicone. The technical case rests on data. Lakera's models learn from a very large stream of adversarial prompts, drawn partly from the Gandalf community game, and that corpus is genuinely hard for a competitor to replicate. Vendor figures of 98%+ detection at sub-50ms latency with under 0.5% false positives are strong if accurate, though we could not verify them. The friction is commercial - nothing is published on pricing, and buying now means Check Point enterprise procurement rather than a credit card.
Full Lakera review →Frequently Asked Questions
What is the main difference between Arthur and Lakera?
Arthur: Teams that want open-source guardrails running inside their own stack with the option of an inexpensive managed tier, and who value published pricing and unlimited seats. Lakera: Teams that want managed, low-latency prompt injection defence with enterprise support and are comfortable with a proprietary API and an enterprise sales process. Both sit in Guardrails & Safety, so the decision usually comes down to billing model and deployment rather than raw capability.
Which is cheaper, Arthur or Lakera?
It depends entirely on your workload shape, because they meter differently - Arthur bills on use-case and Lakera bills on no usage metering. Published starting prices are $60/mo and Not published respectively, but those numbers are not comparable until you apply them to the same traffic. Use our cost calculator to model both against your own request volume and span count.
Can I self-host Arthur or Lakera?
Arthur: Yes, free. Lakera: No or paid tier only. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.