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Software Engineering mercor

Machine Learning Engineer Expert

Mercor • Remote

Education

PhD

Type

Hourly

Pay Rate

$90/hr

Listed

121d ago

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About this role

From the Mercor listing

We’re hiring experienced Machine Learning Engineers and Applied ML Researchers to design, solve, and evaluate complex machine learning challenges that reflect real-world ML workflows. This role requires strong hands-on modeling expertise, the ability to develop high-quality reference solutions, and deep familiarity with modern machine learning techniques across a variety of domains and data modalities.

• Develop end-to-end machine le.arning solutions for challenging prediction and modeling problems

• Analyze datasets and define appropriate modeling approaches, validation strategies, and evaluation metrics

• Perform exploratory data analysis, feature engineering, and data preprocessing

• Train, tune, and evaluate machine learning models across tabular, text, image, and time-series datasets

• Develop strong reference solutions using industry-standard machine learning techniques and best practices

• Review and validate the technical quality of machine learning projects and deliverables

• Document methodologies, assumptions, and evaluation results in a clear and reproducible manner

• Identify opportunities to improve model performance through systematic experimentation and iteration

Develop end-to-end machine le.arning solutions for challenging prediction and modeling problems

Analyze datasets and define appropriate modeling approaches, validation strategies, and evaluation metrics

Perform exploratory data analysis, feature engineering, and data preprocessing

Train, tune, and evaluate machine learning models across tabular, text, image, and time-series datasets

Develop strong reference solutions using industry-standard machine learning techniques and best practices

Review and validate the technical quality of machine learning projects and deliverables

Document methodologies, assumptions, and evaluation results in a clear and reproducible manner

Identify opportunities to improve model performance through systematic experimentation and iteration

• Master’s degree or PhD in Computer Science, Machine Learning, Statistics, Mathematics, Electrical Engineering, or a related field from a top-tier university

• 2+ years of hands-on experience developing, training, evaluating, and optimizing machine learning models in a professional or research setting.

• Strong proficiency in Python and modern machine learning frameworks (e.g., scikit-learn, XGBoost, LightGBM, PyTorch, TensorFlow)

• Demonstrated experience building end-to-end machine learning solutions, including data preparation, model development, validation, and evaluation

• Strong understanding of model evaluation metrics, validation methodologies, and experimental design

• Experience with one or more of the following areas:

Tabular machine learning

Natural language processing

Computer vision

Recommendation systems

Ranking systems

Time-series forecasting

• Tabular machine learning

• Natural language processing

• Computer vision

• Recommendation systems

• Ranking systems

• Time-series forecasting

• Ability to work independently on open-ended machine learning problems and deliver high-quality technical outputs

Master’s degree or PhD in Computer Science, Machine Learning, Statistics, Mathematics, Electrical Engineering, or a related field from a top-tier university

2+ years of hands-on experience developing, training, evaluating, and optimizing machine learning models in a professional or research setting.

Strong proficiency in Python and modern machine learning frameworks (e.g., scikit-learn, XGBoost, LightGBM, PyTorch, TensorFlow)

Demonstrated experience building end-to-end machine learning solutions, including data preparation, model development, validation, and evaluation

Strong understanding of model evaluation metrics, validation methodologies, and experimental design

Experience with one or more of the following areas:

• Tabular machine learning

• Natural language processing

• Computer vision

• Recommendation systems

• Ranking systems

• Time-series forecasting

Tabular machine learning

Natural language processing

Computer vision

Recommendation systems

Ranking systems

Time-series forecasting

Ability to work independently on open-ended machine learning problems and deliver high-quality technical outputs

• PhD from a leading research university

• Experience at leading technology companies, AI labs, research institutions, or high-growth startups

• Participation in competitive machine learning or data science competitions

• Experience optimizing models against performance-based evaluation metrics

• Familiarity with advanced techniques such as ensembling, hyperparameter optimization, transfer learning, foundation model fine-tuning, or reinforcement learning

• Publications, patents, or significant open-source contributions in machine learning or AI

• Experience reviewing, mentoring, or evaluating the work of other machine learning practitioners

PhD from a leading research university

Experience at leading technology companies, AI labs, research institutions, or high-growth startups

Participation in competitive machine learning or data science competitions

Experience optimizing models against performance-based evaluation metrics

Familiarity with advanced techniques such as ensembling, hyperparameter optimization, transfer learning, foundation model fine-tuning, or reinforcement learning

Publications, patents, or significant open-source contributions in machine learning or AI

Experience reviewing, mentoring, or evaluating the work of other machine learning practitioners

We consider all qualified applicants without regard to legally protected characteristics and provide reasonable accommodations upon request.

Requirements

  • Must be eligible to work in Remote
  • Fluent proficiency in English (Written & Verbal)
  • Reliable high-speed internet connection
  • PhD's degree or equivalent professional experience
  • Demonstrated expertise in Software Engineering

How long hiring takes

Across the AI training platforms we refer candidates to, the median gap between referral and hire is about 30 days. It varies by platform and role, so treat it as a rough guide for this one.

Within 2 weeks
~25%
Within 6 weeks
~60%
Within 3 months
~80%

Talent Pool members

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Interview Prep

Sample questions for a Machine Learning Engineer role, written in-house to help you prepare.

How do you choose between a simpler interpretable model and a more complex model that performs marginally better?

The decision depends on how the model's output is used downstream. If a human needs to act on and justify individual predictions, like in lending or healthcare, interpretability often outweighs a small accuracy gain. If the model feeds an automated system where explainability isn't a hard requirement, I'll take the complexity if the performance gain is meaningful and validated, not just noise.

Explain how you would set up a proper train, validation, and test split for a time series problem.

Random splitting leaks future information into training for time series, so I split chronologically instead, training on the earliest period, validating on the next, and testing on the most recent. Any cross-validation also needs to respect time order, using something like rolling-origin validation, rather than standard k-fold, which would otherwise let the model see the future during validation.

What statistical test would you use to determine if an A/B test result is significant, and what assumptions does it rely on?

For a conversion-rate comparison, a two-proportion z-test or chi-squared test is standard, and it assumes independent observations and a large enough sample size for the normal approximation to hold. If the sample is small or the metric isn't binary, I'd switch to a more appropriate test, since applying the wrong test's assumptions is a common source of false confidence in A/B results.

How do you approach hyperparameter tuning efficiently when the model is expensive to train?

I use a coarse random search first to identify the promising region of the hyperparameter space, since grid search wastes compute on combinations unlikely to matter. From there, Bayesian optimization narrows in on the best configuration with far fewer expensive training runs than an exhaustive search would require, which matters a lot when each run is costly.

See all 10 questions for this role →

This listing calls for this tool directly. Prep for the technical screen:

Why this role

At $90/hr, this Machine Learning Engineer Expert position compensates Software Engineering expertise on its own terms, the kind of rate that would otherwise only show up inside a law firm, hospital, or research lab.

Skills and categories

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Common questions

Does it cost money to apply to Mercor?

No, applying and joining Mercor is free. Mercor's revenue comes from a fee it charges the client on top of your hourly rate, not from applicants. Treat any request for payment to join as a red flag.

Is Mercor for freelancers or full-time contractors?

Mercor places you with one client for a defined engagement, like 'Python Tutor for 3 months', rather than having you grab small tasks from a shared queue. Most roles function as steady contract work, not one-off gigs.

What does task-based AI training work look like?

Practical, hands-on data work: recording short videos, categorizing images, rating text responses, or analyzing data. Tasks are designed to be short and distinct, typically 5 to 60 minutes each.

What does asynchronous AI training work mean in practice?

No set hours, no check-ins, no meetings. You log in when you want, pick up an available task, complete it, and submit; nobody is waiting on you in real time. That's different from remote employment, where you're expected online during business hours. The tradeoff: you're competing with others for available tasks, so an empty queue means there's simply nothing to do until more work is released.

What does Software Engineering work look like for a Machine Learning Engineer Expert?

Tasks here are scoped to Software Engineering, not generic labeling. As a Machine Learning Engineer Expert, expect to draw on real domain judgment (evaluating outputs, correcting errors, or providing expert reasoning specific to Software Engineering) rather than following a one-size-fits-all rubric. If you don't have hands-on Software Engineering background, this is likely not the right listing to start with.

What specific skills does this listing call for?

Coding and Python are named directly in the listing. If you don't have hands-on experience with these, expect the screening process to test for them directly rather than accepting adjacent experience as a substitute.

How much does this specific role pay?

This listing is posted at $90/hr, an hourly rate. Pay can change between when we last checked the listing and when you apply, so confirm the current number on the platform's own application page before committing time.

What happens when I click Apply on this listing?

You'll be taken to Mercor's external site to complete your application there. This listing links through a referral, but the process is identical to applying directly; the link just routes you correctly. Create an account on their site and follow their onboarding steps.

Is a PhD required?

For this specific role, yes, or near-equivalent professional depth. The credential gate is enforced at the assessment stage, not just on paper. That said, active PhD candidates and people with equivalent published research have qualified without a formal degree. The assessment is the real filter.

How soon will I start working after applying to Mercor?

Not immediately. Mercor is a talent marketplace, not a task queue, so applying puts you in a pool of candidates. You start working only once a specific client, like a major AI lab, selects your profile, and that matching process can take weeks.