Java Backend Developer — AI Training

About OpenTrain

OpenTrain is the #1 platform for people who build careers in AI training and data labeling. We help contributors find projects, consolidate opportunities, and build a unified portfolio of AI training work they control.

OpenTrain AI is the hiring organization for this role. We connect experienced engineers to software-focused tasks that directly support how modern AI systems are built and maintained.

• A place to grow a durable freelance career in AI training and data labeling
• Work remotely and contribute to real products that shape model behavior

About AI training and this kind of work

AI training (also called data labeling or human feedback work) is the human side of building artificial intelligence. Engineers and contributors prepare, review, and improve the data and systems that modern models learn from.

Many roles in this industry are remote and flexible; they let you apply software engineering skills while influencing how state-of-the-art AI behaves.

• Work directly supports training, evaluation, or deployment workflows for AI systems
• Suitable for experienced engineers who want contract, part-time work with impact

The role

You will design, develop, maintain, troubleshoot, and optimize Java backend components that support AI training systems and integrations. Expect to collaborate with architects, product owners, and QA engineers and to deliver high-quality, well-documented code.

This is a part-time contractor role (20+ hours/week) and fully remote. The position emphasizes reliability, performance, security, and clarity in code and architecture.

• Focus area: Java and Spring ecosystem for backend services
• Work directly on backend integrations, APIs, and scalable systems that feed AI training workflows

What you'll do

• Design and maintain backend components using Java and the Spring ecosystem
• Build secure, scalable software aligned with product and business objectives
• Troubleshoot, debug, and optimize backend processes for performance and reliability
• Participate in code reviews and continuous improvement efforts
• Collaborate with cross-functional teams to implement seamless integrations
• Write clean, well-documented code that meets requirements and standards

Requirements

Candidates must demonstrate expert-level backend development skills and proven experience delivering complex enterprise solutions in Java and Spring.

• Expert-level Java programming and backend development experience
• Strong hands-on experience with Spring and related frameworks
• Solid understanding of RESTful services, microservices architecture, and API design
• Experience reviewing, debugging, and optimizing enterprise backend code
• Ability to work independently in a remote team setting with excellent written and verbal communication

Helpful background

The following experience is a plus but not strictly required: integrating Java applications with DevOps tooling and cloud platforms, performance tuning for high-traffic systems, and prior work on distributed agile teams serving global customers.

• Experience with cloud platforms and DevOps integrations
• Background in performance tuning for high-traffic, distributed systems
• Experience on distributed, agile teams

Compensation, schedule, and logistics

Pay is hourly (PAY_PER_HOUR) with a stated range of $20–$50 per hour; the role commonly aligns to about 20+ hours per week. The position is offered as a part-time contractor engagement and is open to candidates worldwide who can work in English.

• Rate range: $20–$50 USD per hour
• Time commitment: 20+ hours/week (part-time, contractor)
• Language: English required; location: worldwide

How it works

Create an OpenTrain profile, highlight your Java and backend experience, and apply. As a contractor you will deliver agreed work, collaborate with teammates, and follow project guidelines for quality and security.

OpenTrain makes it easy to manage multiple AI training engagements and build a portfolio of related work over time.

• Prepare examples of Java/Spring work or links to portfolio/code samples
• Apply with a clear summary of relevant backend experience and availability