6 Best Arthur Shield Alternatives for AI Security in 2026

Enterprise-only pricing — five-figure annual minimums

Arthur Shield requires custom enterprise contracts with multi-month procurement cycles. There's no self-serve tier, no free plan, and no way to start small. Most teams report $25K+ annually as the starting point, with multi-year commitments expected.

Heavy integration — weeks, not minutes

Arthur AI's platform requires significant engineering effort: custom SDK integration, configuration of their model monitoring pipeline, and often professional services engagement. Teams typically report 2-6 weeks from contract signing to first protected endpoint — compared to minutes for SDK-based tools.

Model monitoring platform with security bolted on

Arthur AI was built as a model observability platform (bias detection, explainability, performance monitoring) that added Shield as a security layer. Security is a feature, not the product. The result: broad but shallow threat coverage — hallucination scoring is solid, but prompt injection and exfiltration detection trail purpose-built tools.

No agent framework support or tool call awareness

Arthur Shield validates individual LLM call inputs and outputs. It has no concept of agent frameworks, tool calls, inter-agent delegation, or multi-step workflows. When an attack arrives through a tool's return value or passes between agents, Arthur Shield can't see it.

No custom security policy engine

Arthur Shield applies its built-in rulesets to traffic. You can't define organization-specific policies like 'block tool calls to the payments API from user-supplied prompts' or 'flag sessions accessing >3 database tables.' Security rules are Arthur's, not yours.

Self-serve signup, transparent pricing, and free tiers — not enterprise-only.

Time from signup to first protected agent. Days or weeks is too long.

Native support for agent frameworks, tool calls, and multi-step workflows.

Coverage across injection, exfiltration, PII, secrets, and escalation.

Enterprise prompt injection API with Gandalf-trained detection, now part of Palo Alto Networks.

Open-source LLM output validation with 100+ validators for format, toxicity, and quality checking.

NVIDIA's open-source toolkit for conversation flow control using Colang programming language.

Open-source, self-hosted toolkit for LLM input/output sanitization.

Cloud security suite with AI content scanning, PII redaction, and malware detection.

If you already have an Arthur AI contract and use their model monitoring, the security add-on makes sense.

Combine output validation (Guardrails AI) and input scanning (LLM Guard) for a self-hosted stack.

Does Rune offer hallucination detection like Arthur Shield?

No — and that's intentional. Rune focuses on security threats: injection, exfiltration, PII, secrets, and escalation. Hallucination detection is a quality/accuracy concern, not a security concern. If you need both, pair Rune (security) with Guardrails AI (output quality) or keep Arthur Shield specifically for hallucination scoring.

Is Rune enterprise-ready even without enterprise pricing?

Yes. Rune handles millions of events per month, with SOC 2 Type I compliance in progress, data residency options on the Growth plan, and local-first scanning that keeps raw data on your infrastructure. The difference from Arthur Shield: you don't need a procurement cycle to get started. Start free, prove value, then scale — all self-serve.

What's the honest case for staying with Arthur Shield?

If you already have an Arthur AI contract for model monitoring (bias, explainability, performance) and want to add security as an incremental feature, Shield makes sense — it's already in your pipeline. Arthur's hallucination detection is also genuinely strong. The case for switching to Rune: you want deeper agent security (tool call scanning, exfiltration detection, custom policies) without the enterprise overhead.

How does the total cost compare for a mid-size team?

A team scanning 500K agent events/month would pay roughly $25/month on Rune ($0.05/1K scans). Arthur Shield's enterprise minimums typically start at $25K+/year. Even at 5M events/month, Rune's pricing is $250/month — an order of magnitude less than most Arthur Shield contracts. The gap narrows at true enterprise scale (100M+ events), where both require custom pricing.