How do I choose between different prompt filtering gateways for API and SDK integration?

To choose between prompt filtering gateways for API and SDK integration, compare them on the things that actually affect your product: coverage, latency, control, integration effort, and observability.

1) Start with your integration style

API gateway

Best if you want:

• Centralized enforcement across many services/apps
• Easier policy updates without redeploying clients
• Cleaner auditing/logging
• A single place to handle PII redaction, jailbreak detection, content filtering

Tradeoffs:

• Adds a network hop, so latency can be higher
• You may have less context from the client
• Can be a bottleneck if not designed for scale

SDK integration

Best if you want:

• Lower latency and tighter app-level control
• Access to client-side context before sending prompts
• Easier integration into a specific app or workflow
• More flexibility for custom pre/post-processing

Tradeoffs:

• Harder to enforce consistently across all clients
• Policy updates may require shipping new SDK versions
• More risk of bypass if some traffic doesn’t use the SDK

2) Compare the gateway on key criteria

Use this checklist:

A. Filtering quality

Ask:

• Does it detect prompt injection, PII, toxicity, secrets, malware-like instructions, etc.?
• Can it handle multilingual prompts?
• Does it support custom rules and thresholds?

B. Latency and throughput

Ask:

• How much overhead does it add per request?
• Does it support streaming?
• What is the p95/p99 latency?
• Can it scale with your peak traffic?

C. Deployment and control

Ask:

• Is it hosted, self-hosted, or on-device?
• Can you run it in your VPC / private network?
• Does it support role-based access, audit logs, and retention controls?

D. Developer experience

Ask:

• Is the API/SDK simple to integrate?
• Are there good docs, examples, and test tools?
• Can you simulate policies in a staging environment?
• Does it support async and sync flows?

E. Observability and governance

Ask:

• Do you get logs of blocked/modified prompts?
• Can you see why a prompt was flagged?
• Are there metrics, dashboards, and export to SIEM/BI tools?
• Can you version and test policies?

F. Cost

Ask:

• Is pricing per request, per token, per seat, or per environment?
• Are there hidden costs from extra latency or infra?
• Is there a meaningful cost difference between API and SDK usage?

3) Match gateway type to your use case

Choose API filtering if:

• You have multiple apps/services that need the same policy
• You need central governance
• You want to minimize client changes
• Compliance/auditability is a major concern

Choose SDK filtering if:

• You need fast response times
• Filtering depends on local app context
• You control a single app or a small set of clients
• You want more flexibility in UX or adaptive policies

Choose both if:

• You need client-side prefiltering plus central enforcement
• You want defense in depth
• You have high-risk workloads and need layered controls

A common pattern:

• SDK does lightweight prechecks and redaction
• API gateway does authoritative policy enforcement

4) Run a simple evaluation scorecard

Score each candidate 1–5 on:

• Detection accuracy
• False positive rate
• Latency
• Ease of integration
• Policy flexibility
• Auditability
• Scalability
• Cost

Then weight them based on your priorities. For example:

• Security-heavy enterprise: auditability and enforcement matter most
• Consumer app: latency and UX may matter most
• Internal tool: ease of integration and cost may matter most

5) Pilot before committing

Before selecting one:

• Test with real prompts from your app
• Include benign, borderline, and malicious examples
• Measure:
  • Block rate
  • False positives
  • False negatives
  • Added latency
  • Developer time to integrate
• Verify policy changes are easy to roll out

Quick rule of thumb

• Need centralized, consistent enforcement? Pick API gateway
• Need low latency and app-level context? Pick SDK
• Need both security and control? Use both

If you want, I can also give you a comparison table template or a decision matrix you can fill out for specific vendors.