AI Engineer

About The Company

America is under sustained cyber attack. Our adversaries infiltrate our networks, steal our intellectual property, and degrade the digital infrastructure that modern life depends on. These malicious activities often go unpunished, creating a significant threat to national security and economic stability. Recognizing the critical need for robust cybersecurity measures, Twenty was founded in 2024 with a mission to elevate the United States and its allies' dominance in cyberspace. Headquartered in Arlington, Virginia, Twenty specializes in industrializing offensive cyber operations to deter adversaries and strengthen national security. Backed by notable investors such as Accel, Caffeinated Capital, Friends & Family Capital, Point72 Ventures, General Catalyst, and In-Q-Tel, the company has raised $138 million to develop innovative cyber capabilities that ensure deterrence and security in the digital age.

About The Role

We are seeking a highly skilled and motivated Machine Learning Engineer to join our team. In this role, you will be responsible for building and deploying language-model-powered systems that enhance Twenty’s mission-critical cyber capabilities for U.S. national security. You will oversee the entire lifecycle of AI development—from curating specialized datasets and fine-tuning models to deploying reliable inference and retrieval systems in production environments. This position requires close collaboration with product and engineering teams to translate operational needs into high-performing AI features. The environment is dynamic, operating across both cloud and on-premises infrastructure, where speed, accuracy, and security are paramount. Your work will directly contribute to safeguarding national security and maintaining technological superiority.

Qualifications

• Minimum of 4+ years of professional experience in software development, specifically supporting ML/AI-enabled applications.
• Strong proficiency in Python and extensive experience with deep learning frameworks such as PyTorch, TensorFlow, or JAX.
• Hands-on experience with large language model (LLM) post-training techniques, including continued pre-training, supervised fine-tuning (SFT), reinforcement learning with human feedback (RLHF), and other alignment methods like DPO, PPO, or GRPO.
• Proficiency in curating, cleaning, and preprocessing datasets for training and evaluation purposes.
• Working knowledge of relational, graph, and vector database concepts, including experience with tools like pgvector, ChromaDB, Pinecone, Milvus, or Weaviate.
• Experience designing and implementing evaluation metrics and testing procedures for LLMs and intelligent agents.
• Ability to integrate LLM and agent systems using frameworks such as Pydantic-AI, LangChain/LangGraph, or CrewAI.
• Bachelor’s degree in Computer Science, Software Engineering, or a related field, or equivalent practical experience.

Responsibilities

• Create, maintain, and refine high-quality datasets for training and evaluating specialized AI models tailored to cybersecurity applications.
• Fine-tune language models, ranging from small specialized models to medium-sized foundation models, aligned with mission requirements.
• Implement post-training and alignment strategies to enhance model performance, reliability, and safety.
• Develop retrieval-augmented generation (RAG) systems that ground model outputs using external knowledge bases to improve accuracy and contextual relevance.
• Design, develop, and optimize model serving infrastructure to support scalable, secure, and efficient deployment in production environments.
• Establish evaluation frameworks and testing harnesses to measure model quality, latency, and regression performance.
• Integrate AI capabilities into operational workflows and applications using modern orchestration frameworks and APIs.
• Collaborate with cross-functional teams—including product managers, engineers, and security specialists—to identify high-impact use cases and deliver innovative solutions.
• Document models, datasets, and operational procedures clearly and comprehensively to facilitate ongoing maintenance and knowledge sharing.

Benefits

• Health coverage including medical, dental, and vision plans, along with life, AD&D, and disability insurance options.
• Paid parental leave for eligible full-time employees—12 weeks for birthing parents, 4 weeks for non-birthing parents, and 6 weeks for adoptive, foster, or surrogacy arrangements.
• Flexible paid time off, including paid holidays, allowing employees to take time as needed for personal and family commitments.
• Retail plans featuring a 401(k) with pre-tax and Roth options, along with HSA/FSA and dependent care FSA options to support long-term financial planning.
• On-site amenities such as garage parking, bike storage, a fitness center, and a stipend for desk setup to promote a comfortable and productive work environment.

Note

Note that benefits may vary based on location, role, and eligibility. Detailed information will be provided during the interview and offer process.

Equal Opportunity

Twenty is an equal opportunity employer. We are committed to fostering an inclusive environment and consider all qualified applicants without regard to race, color, religion, sex, sexual orientation, gender identity, national origin, age, veteran status, disability, or any other protected characteristic. We believe diversity enriches our team and enhances our ability to serve our mission.