Senior Full-Stack Engineer, Autonomous Defense

About this role

Build the platform that runs autonomous defensive agents across customer environments. The role combines distributed backend systems, safe execution and change management, and operator-facing interfaces that make agent behavior visible and controllable.

About the company

Horizon3.ai is a technology company specializing in cybersecurity solutions, focusing on automated penetration testing and threat detection for enterprises. They provide a range of services aimed at enhancing security posture and risk management for organizations across various sectors.

The team

Autonomous Defensive team, collaborating with AI researchers, attack engineers, and product.

Stack

What you'll do

• Build a durable agent execution runtime with resumable workflows, checkpointing, cancellation, and timeouts.
• Develop a versioned agent tool registry with schema validation and server-side authorization.
• Create connectors for security control planes such as EDR, firewalls, identity, SIEM, and cloud IAM.
• Implement safe-change workflows with simulation, approval gates, staged rollout, rollback, and audit trails.
• Build React and TypeScript interfaces and streaming data flows for long-running agent activity.
• Extend tenant isolation for agent write actions, including execution boundaries, egress control, and quotas.
• Develop ETL and GraphQL features, including pipelines that produce research and evaluation datasets.
• Instrument agent runs with distributed tracing and per-tenant cost and token accounting.

What we're looking for

• Bachelor's degree in Computer Science, Computer Engineering, or a related field.
• At least 7 years of professional software engineering experience.
• Production experience with React, TypeScript, modern CSS, and backend APIs, especially GraphQL.
• Experience with cloud platforms and containers such as Docker and Kubernetes.
• Expert SQL proficiency.
• Production distributed-systems experience, including asynchronous workflows, queues, retries, idempotency, and partial failure.
• Track record of operating production services and owning on-call responsibilities.

Nice to have

• Production experience building agentic or LLM-backed systems.
• Experience with durable execution or workflow engines such as Temporal.
• Experience building multi-tenant platforms with strict isolation and short-lived credential brokering.
• Experience integrating third-party APIs and security control planes.
• Experience with relational and graph databases, GraphQL backends, and client-side streaming patterns.
• Experience building operator-facing interfaces where auditability and safe actions are critical.
• Familiarity with observability tools and distributed tracing.
• Awareness of prompt injection and untrusted-input handling.

Benefits

• Equity package in the form of stock options.
• Health, vision, and dental insurance for employees and their families.
• Flexible vacation policy.
• Generous parental leave.