Senior Backend Platform Engineer – Defensive Agent Runtime

Horizon3; United States; Remote; USD 150,000 - 210,000; Full time

Benefits offered by this job

Growth opportunities

Innovation-driven culture

Flexible remote work

Inclusive and diverse team

Job summary

Horizon3 seeks a Senior Backend Engineer for the Defensive Agent platform. You will own the agent execution runtime, the tool layer, and the observability that makes agent behavior debuggable across thousands of tenants.

You will work with AI researchers to build a safe, shippable substrate rather than tuning prompts. The role emphasizes durable workflows, per-tenant security, a registry with versioning, and integration with third-party security control planes.

Qualifications

• 7+ yrs professional software engineering experience with OO or functional languages.
• Expert proficiency in SQL and relational/graph databases.
• Track record of shipping and operating production services with on-call ownership.
• Experience designing distributed systems with asynchronous workflows, retries, idempotency, and partial failure.
• Experience building apps on AWS/Azure/GCP with Docker and Kubernetes.
• Experience with durable execution/workflow engines (Temporal) or equivalent checkpointing.
• Experience building agentic or LLM-backed systems in production.
• Experience multi-tenant platforms with strong isolation and short-lived credentials.
• Familiarity with security control planes and APIs (EDR, firewalls, SIEM, IAM).
• Experience GraphQL backends and observability tooling (Datadog, Prometheus, Grafana).
• Awareness of prompt injection and untrusted data handling.

Responsibilities

• Own the agent execution runtime, including durable, long-running workflows with checkpointing and timeouts.
• Design and implement the tool layer and registry with per-tenant enablement and server-side authorization.
• Build a connector framework for security control planes (EDR, firewall, IAM) and audit trails.
• Develop ETL/GraphQL capabilities for agent context, run history, and remediation state.
• Instrument systems with distributed tracing and cost/token accounting for tenant isolation.

Skills

Python

Go

Scala

TypeScript

C++

SQL

GraphQL

Distributed systems

Cloud platforms

Docker

Kubernetes

Temporal

Multi-tenant

Security awareness

Education

Bachelor's degree in CS/CE or related field

Tools

PostgreSQL

Neo4j

Datadog

Prometheus

Grafana

Temporal

GraphQL tooling

Job description

Horizon3 seeks a Senior Backend Engineer for the Defensive Agent platform. You will own the agent execution runtime, the tool layer, and the observability that makes agent behavior debuggable across thousands of tenants.

You will work with AI researchers to build a safe, shippable substrate rather than tuning prompts. The role emphasizes durable workflows, per-tenant security, a registry with versioning, and integration with third-party security control planes.