Senior Software Engineer

About the role

You will own the core architecture and evolution of the Fuzzer, the autonomous search engine that drives Antithesis's mission to verify software reliability through deterministic simulation. In this role, you will design and implement the orchestration logic that explores vast system state spaces and actively seeks out failure modes across simulated environments. You will be responsible for making the Fuzzer measurably smarter by improving code coverage, search efficiency, and the breadth of bugs it can automatically discover over time. You will craft stable, clean interfaces that allow external systems, including machine learning models and AI agents, to plug in and dynamically configure search strategies. You will instrument deep observability and build rigorous benchmarking suites that illuminate Fuzzer behavior and directly inform product decisions. You will translate complex technical tradeoffs into clear design documents and mentor engineers to elevate the overall quality and long-term vision of the product. Ultimately, your work will directly define how reliably software can be built and will solve some of the most consequential unsolved problems in verification today.

Key facts

What you'll do

• Own the end to end lifecycle of core Fuzzer functionality, including orchestrating how systems under test are explored, injecting controlled chaos, and navigating complex state spaces to discover bugs inside simulated environments.
• Make the Fuzzer intelligently adaptive by implementing strategies to improve code coverage, refine search efficiency, and expand the variety of bug classes it can reliably uncover during continuous execution.
• Design and deliver clean, stable, and well documented interfaces that allow the rest of the product ecosystem and external systems such as ML models and AI agents to plug in seamlessly and configure search behavior at scale.
• Build comprehensive observability dashboards and benchmarking frameworks that capture Fuzzer behavior in fine detail, using empirical data to guide prioritization and validate the impact of new ideas.
• Write clear, high quality design documents that capture assumptions, tradeoffs, and future directions, ensuring that decisions are understandable long after you have moved on from a feature.
• Mentor engineers across the team by providing thoughtful code reviews, pairing on difficult problems, and elevating the overall standard of engineering practices for reliability critical systems.
• Contribute directly to the long term product roadmap by evaluating new research directions, estimating their feasibility, and translating them into executable plans that the team can ship against.
• Collaborate closely with researchers, product managers, and other engineers to align the Fuzzer with evolving customer needs and the broader goals of Antithesis.
• Champion best practices in software testing by driving initiatives that raise the bar for correctness, reproducibility, and transparency across the entire stack.
• Continuously reflect on the limitations of current approaches and propose experiments that stress test the Fuzzer under extreme or edge case conditions to uncover hidden risks.

Requirements

• Bring 5 or more years of engineering experience working on complex systems in industry or research settings, with a track record of delivering reliable solutions under demanding constraints.
• Demonstrate strong proficiency in Rust, Go, C++, or equivalent systems programming languages, writing safe, performant, and idiomatic code as a standard habit.
• Apply solid CS fundamentals in data structures, algorithms, and systems design, consistently solving problems from first principles rather than relying on inherited patterns.
• Design clean interfaces between complex subsystems and communicate intricate technical ideas clearly to both specialist and non specialist audiences.
• Show a genuine passion for software testing and correctness, whether through building testing infrastructure, contributing to tooling, or spending significant time thinking about why software is inherently buggy.
• Thrive in an in person work environment in Vienna, VA, where trust is built through collaboration and deep technical discussion.
• Be comfortable working autonomously on ambiguous problems where the right approach is not immediately obvious and must be discovered through exploration and experimentation.
• Align with Antithesis culture of rigor, ownership, and intellectual honesty, where the best ideas win regardless of who proposes them.

Nice to have

• Experience with fuzz testing frameworks such as libFuzzer, AFL, or Honggfuzz, and understanding of how coverage guided feedback can drive automated bug discovery.
• Familiarity with property based testing tools like QuickCheck, Hypothesis, or PropTest, and interest in combining generative testing with search based strategies.
• Background in program analysis or formal methods, including techniques for reasoning about program correctness at scale.
• Exposure to ML or AI driven search methods, and curiosity about how learning based policies can complement traditional search algorithms.
• Experience with deterministic replay or record and replay debugging, and the ability to leverage precise execution history for bug isolation.
• A history of meaningful open source contributions to testing tools, compilers, or infrastructure that directly improves the reliability of software.

Practical notes

• This position requires in person presence in the office located in Vienna, Virginia, USA.
• Travel is not expected as part of this role.
• Employment is contingent on authorization to work in the United States, and sponsorship is not indicated at this time.
• The posting remains open until the role is filled, encouraging continuous review of candidates.