What are the main LLM Prompt Injection & AI Application Firewall vendors?

Representative vendors include Lakera Guard, WitnessAI, Aim Security (AI-Firewall), Polaxis. B4 Pro scores the full set.

AI & Machine Learning · Engineering, IT & AI

Should you build or buy LLM Prompt Injection & AI Application Firewall (Runtime Guard)?

LLM Prompt Injection & AI Application Firewall (Runtime Guard) software intercepts incoming requests to LLM-powered applications and evaluates them for prompt injection attacks, jailbreak attempts, and adversarial inputs before they reach the model. It acts as a security layer between untrusted user input and the production AI system.

The build-vs-buy decision for LLM Prompt Injection & AI Application Firewall turns on whether your application's threat model requires documented vendor controls and live threat intelligence or whether a classifier your team controls is sufficient; the volume of requests and your security engineering capacity decide it.

Domain: AI & Machine Learning
Function: Engineering, IT & AI
Industries: Cross-industry

Last assessed June 2026 · re-scored quarterly via The Continuum.

Build it, buy it, or bridge?

	Build it	Buy it	Bridge (buy, then extend)
Cost shape	LLM-as-classifier per request; costs scale with request volume like any model call	Per-request vendor fees that compound at high injection-detection volume	Vendor for initial protection; replace with custom classifier when per-request cost bites
Time to value	A secondary LLM call for input evaluation can be running within a day	Same-day integration with managed threat intelligence and tuned defaults	Vendor defaults running while internal classifier is fine-tuned for false-positive reduction
Differentiation captured	Domain-specific false-positive tuning for your application's input patterns	Generic detection patterns identical across all customers	Vendor base detection with custom threshold tuning for your domain
AI feasibility today	Fine-tuned classifiers and LLM-based guards are well-documented and replicable	Vendor threat intelligence tracks new attack patterns teams don't staff to research	OSS PromptGuard base with vendor threat feed for emerging attack patterns
Who it fits	Teams with security engineering capacity and high-volume customer-facing applications	Teams needing compliance documentation and live threat intelligence	Organizations with some security capacity but reliance on vendor research for new threats

The B4 call

B4 has a verdict for LLM Prompt Injection & AI Application Firewall (Runtime Guard).

Build, Buy, Bridge, or Beware, with the five-dimension scorecard and the reasoning behind it. Unlock the call, and every other category, with B4 Pro.

Unlock the verdict in B4 Pro →

When building LLM Prompt Injection & AI Application Firewall (Runtime Guard) makes sense

The detection mechanism is well-understood and documented. A secondary LLM call that evaluates an incoming input against a jailbreak/injection prompt, or a fine-tuned classifier trained on adversarial examples, is something multiple security teams have shipped to production. Lakera Guard's core is a fine-tuned classifier — the approach is replicable. The build case gets serious when injection detection is high-volume enough that per-request vendor pricing becomes a real cost, when the application's input domain is specialized enough that vendor default classifiers produce unacceptable false-positive rates, and when the organization has a security engineering function that can own the classifier and its retraining cycle. The open-source ecosystem, including PromptGuard and several published implementations, has made self-hosting credible. The main thing you give up when building is continuous threat intelligence — vendors monitor new attack patterns; a self-built classifier reflects the threat landscape at training time.

When buying LLM Prompt Injection & AI Application Firewall (Runtime Guard) makes sense

Buying earns its keep when the application is customer-facing and compliance requirements demand a documented security control that procurement and legal can review. Vendors like Lakera Guard and Aim Security offer out-of-box integration, tuned defaults, and threat intelligence that tracks new injection and jailbreak techniques as they emerge — without requiring internal security research to keep the detection model current. For teams without dedicated security engineering, the operational lift of building and maintaining a classifier is non-trivial. The managed solution also comes with audit logs and reporting that compliance frameworks often require. If your application handles sensitive data and a successful prompt injection would have serious consequences, vendor accountability and continuous threat monitoring are worth real money even if the core detection technique is technically replicable.

Runtime guards for prompt injection, jailbreaks, and adversarial inputs are technically accessible to any team with LLM experience. The detection mechanism, a fine-tuned classifier or a secondary LLM call that evaluates the input before it reaches the main model, is well-documented and has been replicated internally at multiple organizations. Vendors like Lakera Guard and Aim Security offer managed versions of the same approach.

Buying earns its keep when the application is customer-facing, compliance requirements demand documented controls, and the team wants threat intelligence that tracks new attack patterns without internal security research. The build case gets serious when injection detection is high-volume and per-request vendor pricing becomes a real cost, the organization already has a security engineering function that can own a classifier, and false-positive tuning for a specific domain is important enough to warrant control over the detection model. The open-source ecosystem, including PromptGuard and several custom classifier implementations, has made self-hosting credible for teams with security engineering capacity.

Representative vendors

Lakera GuardAim Security (AI-Firewall) and 3 more, scored in B4 Pro

B4 Pro

Get B4's actual call on LLM Prompt Injection & AI Application Firewall (Runtime Guard)

→ B4's call for LLM Prompt Injection & AI Application Firewall (Runtime Guard): Build, Buy, Bridge, or Beware
→ The five-dimension scorecard and the scoring rationale
→ All 5 vendors with pricing and positioning
→ Quarterly re-scores that feed the MCP live, so your agents always query the current call
→ MCP server plus API and SDK access, and CSV/JSON export

Upgrade to B4 Pro

Prefer to read first? The book covers the framework end to end.

Frequently asked

What is LLM Prompt Injection & AI Application Firewall (Runtime Guard)?: LLM Prompt Injection & AI Application Firewall software intercepts incoming requests to AI applications and evaluates them for prompt injection attacks, jailbreak attempts, and adversarial inputs before they reach the model — acting as a security layer between untrusted user input and the production system.
When does building LLM Prompt Injection & AI Application Firewall make sense?: Building makes sense when injection detection volume is high enough that per-request vendor fees are a real cost, and when the security engineering team can own a classifier and its retraining cycle — an approach multiple teams have documented.
When does buying LLM Prompt Injection & AI Application Firewall make sense?: Buying makes sense when compliance requires documented vendor controls, when the team lacks dedicated security engineering, or when continuous threat intelligence tracking new attack patterns is more important than cost optimization.
What are the main LLM Prompt Injection & AI Application Firewall vendors?: Representative vendors include Lakera Guard, WitnessAI, Aim Security (AI-Firewall), Polaxis. B4 Pro scores the full set.

The B4 Index scores every software category on two axes, strategic differentiation and AI feasibility, to classify it Build, Buy, Bridge, or Beware. See the full methodology.

More in AI & Machine Learning

Build or buy AI Code Generation? Build or buy AI Agent Frameworks & Orchestration? Build or buy Vector Database? Build or buy LLM Gateway & Routing? Build or buy AI Guardrails & Safety? Build or buy MLOps / LLMOps Platform? Build or buy Prompt Management & Engineering Platform? Build or buy AI Observability & Evaluation? Build or buy Synthetic Data Generation? Build or buy Data Labeling & Annotation? Build or buy AI Governance & Compliance? Build or buy RAG Infrastructure & Retrieval?

The Build Report

Bi-weekly analysis of software categories through the B4 Framework. What to build, what to buy, and how to use AI to make better decisions for your company.