Our Open-Source RegTech Stack: From €5,400/mo to €800/mo (80% Cost Reduction)

We built Kyonis , an agent-native KYC/AML compliance API. Before writing a single line of code, we made a critical decision: 100% open-source stack . The result? An 80% reduction in infrastructure costs compared to a proprietary stack. Here's exactly what we use and why. The Cost Comparison Component Proprietary Open-Source Savings Cloud hosting €3,000/mo (AWS) €400-800/mo (Scaleway) 75% LLM/AI €1,500/mo €200-400/mo (local + API) 80% Monitoring €500/mo (Datadog) €0 (Grafana) 100% Cache €100/mo (Redis Cloud) €0 (Valkey) 100% Search €200/mo (Elastic) €0 (PostgreSQL pg_trgm) 100% API Gateway €100/mo (Kong) €0 (Traefik) 100% Total €5,400/mo €800-1,200/mo ~80% That's €75,000 saved over 18 months . Our Stack Backend: FastAPI + Go The API layer uses FastAPI (Python) for its async capabilities and auto-generated OpenAPI docs. But for sanctions screening — where we need sub-500ms response times across 100K+ entries — we use a Go microservice with in-memory fuzzy matching. Why not all Go? Becaus