Staff ML Engineer, Agent Training & Environments

Fdetimes; San Francisco (CA); On-site; USD 250,000 - 280,000; Full time

Job summary

Labelbox is seeking an engineer to shape frontier AI by building scalable RL infrastructure and post-training workflows. You will run experiments, create environments agents interact with, and build verifiers to assess success at scale, while delivering reliable, producible platform components.

The role combines systems engineering with agent-focused post-training tasks, demanding strong Python expertise and a pragmatic, high-velocity startup mindset.

Qualifications

• 3+ years of experience shipping systems used by customers and engineers.
• High throughput with high quality; ship a lot, review a lot, and establish a solid foundation.
• Strong system and API design judgment requiring decisive architectural calls.
• Production-grade code is expected daily; know how to keep it reliable.
• Build the substrate others rely on — tooling, CI, harnesses, libraries.

Responsibilities

• Design and implement RL environments for agentic tasks including tool surfaces, state/reset semantics, and rewards.
• Develop verifiers and graders, rubric pipelines, and scalable pass@k scoring.
• Create fine-tuning pipelines turning evaluation data into model improvements (SFT & RL).
• Build eval systems to measure model and product quality across millions of agent trajectories.
• Develop training and serving infrastructure to scale workload and cost accounting.

Skills

Python

System design

API design

Production code

Startup pace

Tools

GraphQL

Kubernetes

GCP

MySQL

PostgreSQL

TypeScript

Job description

Shape the Future of AI

At Labelbox, we're building the critical infrastructure that powers breakthrough AI models at leading research labs and enterprises. Since 2018, we've been pioneering data-centric approaches that are fundamental to AI development, and our work becomes even more essential as AI capabilities expand exponentially.

About Labelbox

We're the only company offering three integrated solutions for frontier AI development:

• Enterprise Platform & Tools: Advanced annotation tools, workflow automation, and quality control systems that enable teams to produce high-quality training data at scale
• Frontier Data Labeling Service: Specialized data labeling through Alignerr, leveraging subject matter experts for next-generation AI models
• Expert Marketplace: Connecting AI teams with highly skilled annotators and domain experts for flexible scaling

Why Join Us

• High-Impact Environment: We operate like an early-stage startup, focusing on impact over process. You'll take on expanded responsibilities quickly, with career growth directly tied to your contributions.
• Technical Excellence: Work at the cutting edge of AI development, collaborating with industry leaders and shaping the future of artificial intelligence.
• Innovation at Speed: We celebrate those who take ownership, move fast, and deliver impact. Our environment rewards high agency and rapid execution.
• Continuous Growth: Every role requires continuous learning and evolution. You'll be surrounded by curious minds solving complex problems at the frontier of AI.
• Clear Ownership: You'll know exactly what you're responsible for and have the autonomy to execute. We empower people to drive results through clear ownership and metrics.

Role Overview

Labelbox is the RL data factory for advancing frontier agent capabilities. We build the data, environments, and evaluations that frontier labs use to train and judge their agents.

This role sits where training meets infrastructure. You will run the experiments and build the systems that run them: environments agents act in, verifiers that decide whether they succeeded, and the fine-tuning pipelines that turn that signal into a better model. We're looking for someone who does both halves — the engineering throughput of a strong platform engineer, and real depth in post-training agents.

The bar is high: engineers with strong judgment who set technical direction, turn prototypes into reliable systems fast, and are at the frontier of agent-first engineering practice.

What you'll work on

• RL environments for agentic tasks: task definitions, tool surfaces, state and reset semantics, reward design — and the harness that runs thousands of them in parallel.
• Verifiers and graders: programmatic checks, LLM judges, rubric pipelines, pass@k scoring. Deciding what "the agent succeeded" means, and making that judgment trustworthy at scale.
• Fine-tuning pipelines that turn evaluation signals into measurable agent improvements — SFT and RL, from data collection through training to checkpoint evaluation.
• Eval systems that run millions of agent trajectories to measure model and product quality.
• Training and serving infrastructure that scales to the throughput frontier labs need: multi-launcher orchestration, long-running job fault tolerance, cost accounting.

What we're looking for

As an engineer

• A 3+ year track record of shipping systems that customers and other engineers still rely on.
• Exceptional throughput, without the quality tax. You ship a lot, you review a lot, and the v1 you ship becomes the foundation the rest of the team builds on.
• Strong system and API design judgment. Hard architecture calls land with you: you make them, defend them under pressure, and update fast when someone else is right.
• You ship production code with coding agents daily. You know where they break and what it takes to make them reliable, and you use that to move the whole team faster.
• You build the substrate other people's work runs on — tooling, CI, harnesses, libraries — and you treat that as the job, not a distraction from it.
• You move fast in ambiguous, startup-pace environments, with influence over authority.
• Deep proficiency in Python, and comfort across the rest of the stack.

As an RL post-training practitioner

• You have fine-tuned models for agentic tasks and made them measurably better. SFT plus at least one RL method (GRPO, PPO, DPO, or similar) in production.
• You have built environments agents operate in, and you know why reward and task design is where most of the difficulty actually lives.
• You have designed verifiers or graders for open-ended work, and you know how they get gamed.
• You debug training runs forensically and methodically.
• You reason about compute-economics. You know what an experiment costs, when a run is not worth finishing, and how to get the same signal for a tenth of the spend.
• You write up what you learned so it changes what the team does next.

Nice to have

• Experience with agent harnesses and coding agents as subjects of training and evaluation.
• Multi-tenancy and isolation for untrusted agent execution: sandboxing, egress control, credential handling.
• Background in production distributed systems, ML infrastructure, or data systems at scale.
• Experience working directly with frontier labs or other highly technical customers.

Our Technology Stack

Our engineering team works with a modern tech stack designed for scalability, performance, and developer efficiency:

• Frontend: React.js with Redux, TypeScript
• Backend: Node.js, TypeScript, Python, some Java & Kotlin
• APIs: GraphQL
• Cloud & Infrastructure: Google Cloud Platform (GCP), Kubernetes
• Databases: MySQL, Spanner, PostgreSQL
• Queueing / Streaming: Kafka, PubSub

Labelbox strives to ensure pay parity across the organization and discuss compensation transparently. The expected annual base salary range for United States-based candidates is below. This range is not inclusive of any potential equity packages or additional benefits. Exact compensation varies based on a variety of factors, including skills and competencies, experience, and geographical location.

Annual base salary range

$250,000—$280,000 USD

Life at Labelbox

• Environment: Fast-paced and high-intensity, perfect for ambitious individuals who thrive on ownership and quick decision-making
• Growth: Career advancement opportunities directly tied to your impact
• Vision: Be part of building the foundation for humanity's most transformative technology

Our Vision

We believe data will remain crucial in achieving artificial general intelligence. As AI models become more sophisticated, the need for high-quality, specialized training data will only grow. Join us in developing new products and services that enable the next generation of AI breakthroughs.

Labelbox is backed by leading investors including SoftBank, Andreessen Horowitz, B Capital, Gradient Ventures, Databricks Ventures, and Kleiner Perkins. Our customers include Fortune 500 enterprises and leading AI labs.

Your Personal Data Privacy: Any personal information you provide Labelbox as a part of your application will be processed in accordance with Labelbox’s Job Applicant Privacy notice.

Any emails from Labelbox team members will originate from a @labelbox.com email address. If you encounter anything that raises suspicions during your interactions, we encourage you to exercise caution and suspend or discontinue communications.