Job description

A model can't act on its own. The harness runs the agent loop, carries context and tools to the model, executes the tool calls it makes, and streams results back reliably. It spans models running on device and larger models in Private Cloud Compute. It handles everything from single-turn requests to long multi-step tasks that span apps, survive interruptions, and resume cleanly. We're looking for a strong systems engineer who is fluent in how LLMs behave. The work is real-time and resource-constrained: responses must start fast enough for a voice assistant to feel instant, under tight latency, memory, and power limits on everything from Mac and iPhone to Apple Watch. Failures rarely have a single cause. In a typical week you might track down why a streamed response stalls, make tool calls cancel cleanly when the user interrupts, or replay a failed request to tell whether the model, the context, or the runtime was at fault. Every change to the harness changes how the model behaves, so we measure our work with evals, not just tests. You'll join the team that owns the core runtime and work alongside senior engineers and researchers. You'll also partner closely with the modeling, tools, and context teams and with app and framework teams across Apple. You'll take features from design through production and grow your ownership of the system over time. You'll use agent harnesses every day while building one for an assistant used by hundreds of millions of people. Bachelor's degree in Computer Science or a related field, with 2+ years of industry experience Strong programming skills in a systems language such as Swift, C++, Rust, Objective-C, or Go Solid foundation in concurrency, inter-process communication, and performance optimization Hands-on experience building LLM-powered systems such as agents, tool calling, or prompt and context design, through professional work or substantial personal projects Daily use of agentic coding tools such as Claude Code, Codex, or Pi, with informed opinions on what makes their harnesses succeed or fail Ability to communicate clearly and make progress on ambiguous problems Experience with Swift and Apple platform development Experience building agent harnesses, orchestration frameworks, or multi-step tool-use systems Experience with model inference integration, streaming protocols, or latency-sensitive client-server systems Experience using evals to diagnose and improve LLM behavior Experience designing APIs or platforms adopted by other engineering teams Familiarity with privacy and security engineering in production systems Active engagement with current research and practice in agent harness design, such as context engineering, tool use, and long-horizon agents, with a record of turning new ideas into practical improvements

Requirements

Must-haves

Bachelor's degree in Computer Science or a related field, with 2+ years of industry experience
Strong programming skills in a systems language such as Swift, C++, Rust, Objective-C, or Go
Solid foundation in concurrency, inter-process communication, and performance optimization
Hands-on experience building LLM-powered systems such as agents, tool calling, or prompt and context design, through professional work or substantial personal projects
Daily use of agentic coding tools such as Claude Code, Codex, or Pi, with informed opinions on what makes their harnesses succeed or fail
Ability to communicate clearly and make progress on ambiguous problems
Experience with Swift and Apple platform development
Experience building agent harnesses, orchestration frameworks, or multi-step tool-use systems
Experience with model inference integration, streaming protocols, or latency-sensitive client-server systems
Experience using evals to diagnose and improve LLM behavior
Experience designing APIs or platforms adopted by other engineering teams
Familiarity with privacy and security engineering in production systems
Active engagement with current research and practice in agent harness design, such as context engineering, tool use, and long-horizon agents, with a record of turning new ideas into practical improvements

Nice-to-haves

None flagged.

Application prep

Use the role’s language and application details while tailoring your materials.

Keywords to mirror

swiftrustgollm

Platform: apple
Effort: medium