Software Engineer, Sandboxing

Mosaic.tech; San Francisco (CA); On-site; USD 300,000 - 450,000; Full time

Benefits offered by this job

Health, dental, vision benefits

Unlimited PTO

Parental leave

Relocation support

Job summary

Thinking Machines is hiring a software engineer to design, build, and operate a sandboxing platform that runs model-generated code and tool calls at scale in San Francisco. You will contribute to secure isolation, scheduling, and observability of thousands of concurrent executions.

The role emphasizes end-to-end ownership, collaboration with researchers and product teams, and delivering fast, reliable, and secure infrastructure that enables researchers to train and deploy agents and tools with

Qualifications

• Bachelor's degree or equivalent in CS, Engineering, or related field.
• Proficiency in Python or Rust for backend development.
• Experience building/operating isolation or virtualization tech.
• Strong knowledge of Linux internals: namespaces, cgroups, seccomp, capabilities, networking.
• Ability to own projects end-to-end in a collaborative environment.
• Thrive in a highly collaborative environment with cross-functional partners.

Responsibilities

• Design, build, and operate sandboxed execution environments for running untrusted, model-generated code and tool calls at scale.
• Improve isolation boundaries using containers, microVMs, or gVisor-style kernels.
• Build scheduling, resource-management, and lifecycle systems for sandboxes under heavy concurrent load.
• Partner with researchers and Tinker's product team to expose sandboxing primitives that are simple to use and hard to misuse.
• Instrument sandboxes for observability and abuse detection, and respond to novel escape or exploitation attempts.
• Own reliability and performance end-to-end from API design down to the virtualization layer.

Skills

Python

Rust

Linux internals

Distributed systems

End-to-end ownership

Education

Bachelor's degree in CS/Engineering

Tools

Kubernetes

Firecracker

Cloud Hypervisor

gVisor

Kata Containers

Job description

About Thinking Machines

The mission of Thinking Machines is to build AI that extends human will and judgment. We are training frontier models with Inkling, developing Tinker to let people make models their own, and crafting interfaces that broaden human-AI communication. We believe the future worth building is human, and we're hiring people who want to build it.

About the Role

Our models and agents increasingly need to run code, use tools, and take actions in the world — safely, reliably, and at scale. The Core Services team builds the sandboxing infrastructure that makes this possible: the isolated execution environments where models write and run code, browse, and interact with tools, both for our researchers during training and for external users building on Tinker.

We're hiring a software engineer to help design, build, and operate this sandboxing platform. You'll work on the systems that isolate and constrain untrusted, model-generated code, and that scale to support thousands of concurrent executions across the company. This is foundational infrastructure: every research experiment and every product surface that lets a model take action depends on it being fast, secure, and dependable.

What You'll Do

• Design, build, and operate sandboxed execution environments for running untrusted, model-generated code and tool calls at scale.

• Improve isolation boundaries using technologies such as containers, microVMs, or gVisor-style kernels, balancing security against startup latency and throughput.

• Build the scheduling, resource-management, and lifecycle systems that provision, reuse, and tear down sandboxes efficiently under heavy concurrent load.

• Partner with researchers and Tinker's product team to expose sandboxing primitives that are simple to use and hard to misuse.

• Instrument sandboxes for observability and abuse detection, and respond to novel escape or exploitation attempts as they're discovered.

• Own reliability and performance of the sandboxing platform end-to-end, from API design down to the underlying virtualization layer.

Skills and Qualifications

Minimum qualifications:

• Bachelor's degree or equivalent experience in computer science, engineering, or similar.

• Proficiency in at least one backend language (we use Python or Rust).

• Experience building or operating isolation or virtualization technology, such as containers, microVMs (e.g. Firecracker, Cloud Hypervisor), or sandboxed runtimes (e.g. gVisor, Kata Containers).

• Solid grounding in Linux internals relevant to isolation: namespaces, cgroups, seccomp, capabilities, and networking.

• Comfort operating across the stack and owning projects end-to-end.

• Thrive in a highly collaborative environment involving many, different cross-functional partners and subject matter experts.

Preferred qualifications:

• Experience securing systems that execute untrusted or adversarial code, including threat modeling and hardening against sandbox escapes.

• Familiarity with running large-scale, multi-tenant infrastructure on Kubernetes or similar orchestration systems.

• Experience with performance-sensitive systems programming and reducing cold-start latency for epithelial compute.

• Track record of contributing to open-source infrastructure or security tooling.

• Interest in how AI agents use tools and code execution, and how that shapes the design of safe execution environments.

Logistics

• Location: This role is based in San Francisco, CA.

• Compensation: Depending on background, skills and experience, the expected annual salary range for this position is $300,000 - $450,000 USD.

• Visa sponsorship: We sponsor visas. While we can't guarantee success for every candidate or role, if you're the right fit, we're committed to working through the visa process together.

• Benefits: Thinking Machines offers generous health, dental, and vision benefits, unlimited PTO, paid parental leave, and relocation support as needed.

As set forth in Thinking Machines' Equal Employment Opportunity policy, we do not discriminate on the basis of any protected group status under any applicable law.

Thinking Machines Lab will consider for employment qualified applicants with criminal histories in a manner consistent with the requirements of the California Fair Chance Act, the San Francisco Fair Chance Ordinance, and any other applicable state or local fair chance ordinance or law.