Senior Backend Engineer, Autonomous Defense

The role

You will build the platform that NodeZero's defensive agents run on, including the runtime, tool layer, orchestration, connector framework and observability. You will work with AI researchers to make their agent work shippable and safe in production across thousands of customer tenants.

What you will do

• Build and own the agent execution runtime: durable, resumable, long-running workflows with checkpointing, idempotent steps, cancellation and timeouts.
• Design the tool layer agents act through, with versioning, schema validation, per-tenant enablement and server-side authorization.
• Build the connector framework for third-party security control planes (EDR, firewall, identity, SIEM, cloud IAM).
• Implement the safe-change pipeline: simulation, blast-radius classification, approval gates, staged rollout, rollback and an immutable audit trail.
• Extend tenant isolation to agents that take write actions, covering execution boundaries, egress control, quotas and cross-tenant leakage.
• Develop product features in ETL and GraphQL for agent context, run history and remediation state.
• Build ETL pipelines that turn pentest and remediation outcomes into datasets for researchers.
• Instrument the platform with distributed tracing, per-tenant cost and token accounting, and debugging tools.
• Partner with AI researchers, attack engineers and product to move capabilities from prototype to production.

Required qualifications

• Bachelor's degree in Computer Science, Computer Engineering or a related field.
• 7+ years of professional software engineering experience in modern object-oriented or functional languages (Python, Go, Scala, C++, TypeScript, etc.).
• Experience building applications on AWS, Azure or GCP using Docker and Kubernetes.
• Expert proficiency in SQL.
• Demonstrated experience designing and operating distributed systems in production: asynchronous workflows, queues, retries, idempotency and partial failure.
• A track record of shipping and operating production services, including on-call ownership.

Nice to have

• Experience building agentic or LLM-backed systems in production.
• Experience with a durable execution or workflow engine (such as Temporal), or having built equivalent checkpointing.
• Experience building multi-tenant platforms with hard isolation, workload identity and short-lived credential brokering.
• Experience integrating many third-party APIs behind a normalized abstraction.
• Familiarity with security control planes and their APIs (EDR, firewalls, SIEM, cloud IAM).
• Experience with PostgreSQL, Neo4j and GraphQL backends.
• Experience with observability tools (Datadog, Prometheus, Grafana) and distributed tracing.
• Awareness of prompt injection and untrusted-input handling in agent systems.

Benefits

• Health, vision and dental insurance for you and your family.
• Flexible vacation policy.
• Generous parental leave.
• Competitive salary and equity.
• Growth and career development opportunities.
• Collaborative, innovative culture.
• Hybrid and remote work options.

Before you apply

• Some roles require regular in-office presence, including roles at the Chicago office.

About the company

Horizon3 is a fast-growing, remote cybersecurity company. Its flagship product, the NodeZero platform, runs production-safe autonomous pentests and assessments across large internal, external, cloud and hybrid cloud environments.