Flo Health

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We are looking for a Machine Learning Engineers to join Flo Health. You will be developing groundbreaking features that leverage our medical expertise, technical skills, rapid adoption of new technologies (like LLMs), product knowledge, and a deep understanding of our users’ needs. If you’re passionate about technology, especially advancements in generative AI, and driven by delivering value to users, we would love to hear from you! Your Experience Must have: - 4+ years of professional experience in the field of machine learning - Demonstrated success in building and deploying large-scale machine learning models; experience with large-scale LLM applications is a bonus - Ability to devise creative solutions to intricate technical challenges, including experience in systems design with the ability to architect and explain ML/LLM pipelines - Strong Python programming skills for efficient model development and deployment - Experience with both traditional ML and modern LLM frameworks - Understanding of the entire ML/LLM development process, including CI/CD, version control, testing, MLOps/LLMOps, and agile methodologies - Experience in building and managing data pipelines using tools like Apache Spark - Excellent communication skills and ability to collaborate with diverse teams - Commitment to responsible AI practices, including fairness, accountability, and transparency Nice to have: - Advanced degree in Computer Science, Mathematics, or a related field - Familiarity with statistical and measurement fundamentals and running and evaluating AB tests - Data visualisation skills - Experience in the MedTech domain What you'll be doing You'll be responsible for: - Explore, develop and test complex ML/AI systems to improve female health - Work with state-of-the-art technologies, such as most advanced LLMs and Generative AI approaches, to build solutions that are medically safe and work at scale - Work in a fast-paced environment to quickly build and validate product hypotheses, taking end-to-end ownership of ML/AI products - Build the future-proof infrastructure for serving Gen AI features at Flo, bringing our AI vision and strategy to life - Constantly improve our technical capabilities by researching and implementing best practices in the context of the fastly evolving space of LLMs - Work in a cross-functional setup alongside other engineering (ML, Backend, QA), product, and analytics teams Annual Salary Range (ranges may vary based on skills and experience) £130,000 - £180,000 GBP How we work We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. What you'll get We support impact with meaningful reward. Here’s what that looks like: - Competitive salary and annual reviews - Opportunity to participate in Flo’s performance incentive scheme - Paid holiday, sick leave, and female health leave - Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents - Accelerated professional growth through world-changing work and learning support - In-person collaboration and work in a hybrid model, with 3 days per week spent in the office - 5-week fully paid sabbatical at 5-year Floversary - Flo Premium for friends & family, plus more health, pension and wellbeing perks Diversity, equity and inclusion Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants .

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We are looking for a Senior AI Engineer with strong LLM and product engineering experience to join our AI Platform team and help ship the AI-driven features across our app — including personalized in-app content recommendations, conversational AI-powered insights, and AI-generated mobile push notifications. You will focus on the product-facing behavior of our GenAI features (relevance, quality, latency, and safety), using the platform’s judges, fine-tuning pipelines, and evaluation tools, and contributing to infrastructure work (Databricks, AWS, Terraform) as initiatives require it. What you’ll do - Feature development: build and ship LLM-powered product features, including AI-generated mobile push notifications, personalized in-app content recommendations and custom user journeys, and conversational AI-powered insights — including structured output such as charts and widgets - Latency and UX: reduce perceived and actual response latency through streaming, pregeneration, and inference-time tradeoffs, working closely with product and design on how AI output is experienced by users - Prompt and model behavior: iterate on prompt design and calibration, use fine-tuned health-domain models (Llama, Gemma, MedGemma) where relevant, and work with the Judge-as-a-Service ecosystem to keep outputs safe and high quality - Experimentation: help enable A/B testing for model and prompt changes, using evaluation gates to ship safely and measure impact - Data and evaluation: contribute to synthetic Q&A generation, golden test sets, and evaluation dataset design that supports the features you’re building - Infrastructure: contribute to Databricks, AWS (EKS), Terraform, or CI/CD work as initiatives require it - Cross-functional impact: collaborate with Product, Security, Analytics, and Medical teams, and engage with technology partners (Databricks, Google, OpenAI, Anthropic, AWS) on pre-release capabilities relevant to your features Experience and skills Must have: - 7+ years of software engineering, with recent hands-on experience building product features backed by LLMs - experience with at least one of: prompt engineering, LLM evaluation, fine-tuning, or model serving - strong Python, and comfort working with APIs/SDKs that wrap LLM calls, prompt templates, and structured outputs - product sensibility: a track record of shipping user-facing features, with attention to latency, tone, and quality of AI output as experienced by end users - comfort picking up new infrastructure tools (Databricks, AWS, Terraform, GitHub Actions) as needed — deep prior expertise not required Nice to have: - LLM evaluation frameworks (judges, graders, calibration methodology) or fine-tuning techniques (LoRA, RLHF/DPO, model distillation) - prompt optimisation frameworks (DSPy or similar) - feature stores or personalization/ranking experience (relevant to in-app content recommendation work) - healthcare, regulated-industry, or safety-critical AI systems experience - data engineering fundamentals (Spark, Delta tables, Parquet) LI-KP1 #LI-Hybrid Annual Salary Range (ranges may vary based on skills and experience) £200,000 - £220,000 GBP How we work We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. What you'll get We support impact with meaningful reward. Here’s what that looks like: - Competitive salary and annual reviews - Opportunity to participate in Flo’s performance incentive scheme - Paid holiday, sick leave, and female health leave - Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents - Accelerated professional growth through world-changing work and learning support - In-person collaboration and work in a hybrid model, with 3 days per week spent in the office - 5-week fully paid sabbatical at 5-year Floversary - Flo Premium for friends & family, plus more health, pension and wellbeing perks Diversity, equity and inclusion Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants .

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We’re hiring a Data Science Lead in London to build and lead our Predictive Growth Optimisation team – pioneering ML models that power our user acquisition strategy, predict lifetime value, and optimise our $25M+ annual marketing spend across channels. This role owns the strategy, development, and continuous improvement of Flo’s pLTV system - a mission-critical model reused across UA, AdTech, personalisation, and financial forecasting. That is the core of the role. Alongside it, you'll stand up a Marketing Mix Modeling (MMM) capability to measure cross-channel effectiveness and inform budget allocation, and develop the algorithms to drive real-time UA campaign management. You'll lead a team building production systems that directly impact our growth trajectory, staying as hands-on as you choose. What you’ll do - Lead & develop a team of 6+ ML and Backend engineers - hiring, mentoring, and setting technical direction - Own pLTV strategy - architect and evolve our core predictive lifetime value models that inform millions in UA decisions - Stand up MMM - build our Marketing Mix Modeling capability: adstock and saturation modelling, channel contribution, and budget allocation, calibrated against our incrementality experiments - Power real-time campaign management - develop the algorithms that optimise our UA campaigns across channels in real time - Build production ML systems - from real-time prediction services handling millions of daily predictions to MMM models - Drive cross-functional impact - partner with Growth, Product, and Finance to translate business problems into ML solutions - Shape technical architecture - guide MLOps infrastructure, monitoring, and rapid iteration cycles - Stay as hands-on as you choose - modeling, architecture decisions, technical problem-solving; your call how deep you go. What you bring Technical Leadership - 7+ years applied ML experience building and deploying models in production - 4+ years managing technical teams (ML engineers, data scientists, or similar) - Expert knowledge of ML fundamentals: supervised/unsupervised learning, time series; strong grounding in causal inference - Experience with modern ML frameworks (TensorFlow, scikit-learn, CatBoost) Growth & Product Experience - Experience with growth analytics, attribution modeling, or marketing effectiveness - Understanding of user acquisition funnels and retention optimization - Comfortable translating business requirements into technical roadmaps - Strong communication skills - can explain complex models to executive stakeholders Production ML Systems - Experience deploying ML models at scale - Knowledge of MLOps practices: model versioning, monitoring, automated retraining - Understanding of data engineering fundamentals and cloud platforms Nice to have - Hands-on experience building Marketing Mix Models end to end, Bayesian or regression based - Background in consumer tech, mobile apps, or health tech - Knowledge of privacy-preserving ML techniques and A/B testing methodology How we work We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. What you'll get We support impact with meaningful reward. Here’s what that looks like: - Competitive salary and annual reviews - Opportunity to participate in Flo’s performance incentive scheme - Paid holiday, sick leave, and female health leave - Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents - Accelerated professional growth through world-changing work and learning support - In-person collaboration and work in a hybrid model, with 3 days per week spent in the office - 5-week fully paid sabbatical at 5-year Floversary - Flo Premium for friends & family, plus more health, pension and wellbeing perks Diversity, equity and inclusion Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants .

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job Flo Health is the world’s most popular women’s health app, supporting over 80 million monthly active users. As our Engineering Manager for the AI Platform , you will lead the core team that builds the shared infrastructure powering every AI feature at Flo—from our chatbot and cycle predictions to personalized health insights. We don’t just use AI; we build the systems that make it possible at scale. You will work in an environment where we maintain direct technical partnerships with Databricks, OpenAI, Anthropic, and AWS, moving far beyond standard vendor relationships. The Environment Our AI Platform team is embedded directly in product delivery, working in cross-functional squads alongside our Data Platform team and external model partners. We operate with a clear but fluid strategy — iterating quickly based on rapid AI/LLM advancements and real-time metrics. You will manage a dynamic environment where roughly 30% of the team's work is reactive, driven by immediate product needs, while maintaining focus on our long-term roadmap. What You’ll Do - Lead & Empower: Manage a team of senior engineers using a distributed leadership model. You’ll provide the management layer that supports their technical execution, performance, and career growth. - Own the Roadmap: Translate product and company goals into clear team roadmaps, managing the balance between structured delivery and the reactive, business-driven work essential to a platform team. - Drive Delivery: Coordinate cross-pod dependencies, resolve blockers, and track roadmap milestones. - Technical Stewardship: Participate in architectural reviews and provide hands-on technical guidance (~20% of your time). You’ll help the team maintain high standards for safety, medical compliance, and performance. - Cross-Functional Impact: Act as the primary point of contact for stakeholders across Product, Analytics, and Engineering, while representing Flo’s AI vision to our industry partners. What you bring: - Engineering Leadership: Proven track record managing engineering teams in fast-moving product environments. You know how to build high-performing teams, mentor talent, and hire effectively. - AI/ML Infrastructure Depth: You have direct, hands-on experience leading or building ML systems in production. You understand MLOps, model serving, or AI platform engineering. - The "Manager-as-Leader" Mindset: You aren't looking to spend your day

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We are looking for a Senior Software Engineer with deep expertise in AI/ML infrastructure to join our AI Platform team and help build the GenAI platform that powers every AI feature at Flo. You will bridge core infrastructure, data engineering, and LLM development to deliver production-grade medical safety judges, fine-tuning pipelines, evaluation frameworks, and real-time personalisation. The team operates 60+ LLM-based evaluation judges, develops proprietary fine-tuned health models, and maintains active partnerships with Databricks, Google, OpenAI, Anthropic, and AWS. What you’ll do - LLM Judge Ecosystem: build and scale Judge-as-a-Service, prompt registries, calibration pipelines, and evaluation orchestration using MLflow 3.x - Fine-Tuning and Serving: develop LoRA/SFT/preference optimisation pipelines for health-domain models (Llama, Gemma, MedGemma) and manage model serving at scale on Databricks - Data and Evaluation Pipelines: build synthetic Q&A generation, golden test sets, reward function engineering, and Delta table schemas in Unity Catalog for reliable, reproducible evaluation data - Infrastructure: maintain Terraform-managed AWS infrastructure (EKS, S3, IAM), Databricks AI Gateway, and CI/CD pipelines (GitHub Actions) with evaluation gates and progressive rollout - Cross-Functional Impact: collaborate with Product, Security, Analytics, and Medical teams, develop internal SDKs and APIs consumed by 5+ teams, and engage directly with technology partners on pre-release capabilities Experience and skills Must have: - Engineering maturity: 7+ years of software engineering, 4+ years focused on ML/AI platforms - LLM experience: recent hands-on work with at least one of: fine-tuning, prompt engineering, LLM evaluation, or model serving - Technical stack: strong Python across production services and data pipelines, data engineering fundamentals (Spark, Delta tables, Parquet) - Platform and infrastructure: Databricks (MLflow, Unity Catalog, Model Serving), AWS (EKS/Kubernetes, IAM), Terraform, GitHub Actions - Cross-domain flexibility: comfort working across ML, data engineering, and infrastructure. You don’t need to be expert in all three, but you contribute wherever the team needs it Nice to have: - LLM evaluation frameworks (judges, graders, calibration methodology) or fine-tuning techniques (LoRA, RLHF/DPO, model distillation)

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job Flo Health is the world’s most popular women’s health app, supporting over 80 million monthly active users. As our Engineering Manager for the AI Platform , you will lead the core team that builds the shared infrastructure powering every AI feature at Flo—from our chatbot and cycle predictions to personalized health insights. We don’t just use AI; we build the systems that make it possible at scale. You will work in an environment where we maintain direct technical partnerships with Databricks, OpenAI, Anthropic, and AWS, moving far beyond standard vendor relationships. The Environment Our AI Platform team is embedded directly in product delivery, working in cross-functional squads alongside our Data Platform team and external model partners. We operate with a clear but fluid strategy — iterating quickly based on rapid AI/LLM advancements and real-time metrics. You will manage a dynamic environment where roughly 30% of the team's work is reactive, driven by immediate product needs, while maintaining focus on our long-term roadmap. What You’ll Do - Lead & Empower: Manage a team of senior engineers using a distributed leadership model. You’ll provide the management layer that supports their technical execution, performance, and career growth. - Own the Roadmap: Translate product and company goals into clear team roadmaps, managing the balance between structured delivery and the reactive, business-driven work essential to a platform team. - Drive Delivery: Coordinate cross-pod dependencies, resolve blockers, and track roadmap milestones. - Technical Stewardship: Participate in architectural reviews and provide hands-on technical guidance (~20% of your time). You’ll help the team maintain high standards for safety, medical compliance, and performance. - Cross-Functional Impact: Act as the primary point of contact for stakeholders across Product, Analytics, and Engineering, while representing Flo’s AI vision to our industry partners. What you bring: - Engineering Leadership: Proven track record managing engineering teams in fast-moving product environments. You know how to build high-performing teams, mentor talent, and hire effectively. - AI/ML Infrastructure Depth: You have direct, hands-on experience leading or building ML systems in production. You understand MLOps, model serving, or AI platform engineering. - The "Manager-as-Leader" Mindset: You aren't looking to spend your day

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job Flo Health is the world’s most popular women’s health app, supporting over 80 million monthly active users. As our Engineering Manager for the AI Platform , you will lead the core team that builds the shared infrastructure powering every AI feature at Flo—from our chatbot and cycle predictions to personalized health insights. We don’t just use AI; we build the systems that make it possible at scale. You will work in an environment where we maintain direct technical partnerships with Databricks, OpenAI, Anthropic, and AWS, moving far beyond standard vendor relationships. The Environment Our AI Platform team is embedded directly in product delivery, working in cross-functional squads alongside our Data Platform team and external model partners. We operate with a clear but fluid strategy — iterating quickly based on rapid AI/LLM advancements and real-time metrics. You will manage a dynamic environment where roughly 30% of the team's work is reactive, driven by immediate product needs, while maintaining focus on our long-term roadmap. What You’ll Do - Lead & Empower: Manage a team of senior engineers using a distributed leadership model. You’ll provide the management layer that supports their technical execution, performance, and career growth. - Own the Roadmap: Translate product and company goals into clear team roadmaps, managing the balance between structured delivery and the reactive, business-driven work essential to a platform team. - Drive Delivery: Coordinate cross-pod dependencies, resolve blockers, and track roadmap milestones. - Technical Stewardship: Participate in architectural reviews and provide hands-on technical guidance (~20% of your time). You’ll help the team maintain high standards for safety, medical compliance, and performance. - Cross-Functional Impact: Act as the primary point of contact for stakeholders across Product, Analytics, and Engineering, while representing Flo’s AI vision to our industry partners. What you bring: - Engineering Leadership: Proven track record managing engineering teams in fast-moving product environments. You know how to build high-performing teams, mentor talent, and hire effectively. - AI/ML Infrastructure Depth: You have direct, hands-on experience leading or building ML systems in production. You understand MLOps, model serving, or AI platform engineering. - The "Manager-as-Leader" Mindset: You aren't looking to spend your day coding, but you have the t

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We are looking for an LLM & AI search Discoverability Manager to shape how Flo is represented across AI systems. This role sits at the intersection of PR, community, content, and AI, owning how our brand is understood, surfaced, and recommended by large language models. Your Main Tasks Will Be Own and optimize Flo’s presence across AI-generated search environments (e.g. ChatGPT, Gemini), ensuring accurate, high-quality brand representation. Monitor how Flo is represented across AI systems, identify gaps or misrepresentation, and proactively act to correct them Build and manage Flo’s reputation across authoritative sources used by LLMs, including Reddit, Quora, and Wikipedia Own Wikipedia strategy and governance, ensuring accuracy, neutrality, and strong positioning as a primary AI citation source Rework and structure Flo’s website as an AI-native source, creating content that answers real user queries and is consistently surfaced in LLM responses Strengthen Flo’s presence in mid-funnel LLM conversations, ensuring the brand is preferred in comparison and evaluation queries Leverage Reddit and Quora as both reputation and discovery channels, shaping narratives and driving qualified organic traffic Build and scale systems for generating and managing external signals (reviews, discussions, third-party content) that influence how LLMs interpret the brand Partner cross-functionally with PR, Product, Social, Customer Support, and Marketing to align messaging and ensure consistency across all external touchpoints We Expect From You 3+ years of experience in online reputation, digital PR, content, or related roles Hands-on experience with or strong understanding of Generative Engine Optimization (GEO) and Answer Engine Optimization (AEO), including how LLMs source, weight, and surface information Understanding of how LLMs source and surface information Hands-on experience with platforms like Reddit, Quora, and Wikipedia Experience shaping brand perception across external, non-owned platforms Strong analytical mindset, connecting reputation signals to business impact Ability to build systems and scale processes, not just execute tasks Strong cross-functional collaboration skills and comfort in fast-moving environments #LI-Hybrid How we work We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. What you'll get We support impact with meaningful reward. Here’s what that looks like: Competitive salary and annual reviews Opportunity to participate in Flo’s performance incentive scheme Paid holiday, sick leave, and female health leave Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents Accelerated professional growth through world-changing work and learning support In-person collaboration and work in a hybrid model, with 3 days per week spent in the office 5-week fully paid sabbatical at 5-year Floversary Flo Premium for friends & family, plus more health, pension and wellbeing perks Diversity, equity and inclusion Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants .

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better. The job We are looking for a Senior Software Engineer with deep expertise in AI/ML infrastructure to join our AI Platform team and help build the GenAI platform that powers every AI feature at Flo. You will bridge core infrastructure, data engineering, and LLM development to deliver production-grade medical safety judges, fine-tuning pipelines, evaluation frameworks, and real-time personalisation. The team operates 60+ LLM-based evaluation judges, develops proprietary fine-tuned health models, and maintains active partnerships with Databricks, Google, OpenAI, Anthropic, and AWS. What you’ll do LLM Judge Ecosystem: build and scale Judge-as-a-Service, prompt registries, calibration pipelines, and evaluation orchestration using MLflow 3.x Fine-Tuning and Serving: develop LoRA/SFT/preference optimisation pipelines for health-domain models (Llama, Gemma, MedGemma) and manage model serving at scale on Databricks Data and Evaluation Pipelines: build synthetic Q&A generation, golden test sets, reward function engineering, and Delta table schemas in Unity Catalog for reliable, reproducible evaluation data Infrastructure: maintain Terraform-managed AWS infrastructure (EKS, S3, IAM), Databricks AI Gateway, and CI/CD pipelines (GitHub Actions) with evaluation gates and progressive rollout Cross-Functional Impact: collaborate with Product, Security, Analytics, and Medical teams, develop internal SDKs and APIs consumed by 5+ teams, and engage directly with technology partners on pre-release capabilities Experience and skills Must have: Engineering maturity: 7+ years of software engineering, 4+ years focused on ML/AI platforms LLM experience: recent hands-on work with at least one of: fine-tuning, prompt engineering, LLM evaluation, or model serving Technical stack: strong Python across production services and data pipelines, data engineering fundamentals (Spark, Delta tables, Parquet) Platform and infrastructure: Databricks (MLflow, Unity Catalog, Model Serving), AWS (EKS/Kubernetes, IAM), Terraform, GitHub Actions Cross-domain flexibility: comfort working across ML, data engineering, and infrastructure. You don’t need to be expert in all three, but you contribute wherever the team needs it Nice to have: LLM evaluation frameworks (judges, graders, calibration methodology) or fine-tuning techniques (LoRA, RLHF/DPO, model distillation) ML data engineering: synthetic data generation, evaluation dataset design, annotation pipelines Healthcare, regulated industry, or safety-critical AI systems experience Prompt optimisation frameworks (DSPy or similar), feature stores (Tecton) #LI-KP1 #LI-Hybrid Annual Salary Range (ranges may vary based on skills and experience) £120,000 - £150,000 GBP How we work We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it. What you'll get We support impact with meaningful reward. Here’s what that looks like: Competitive salary and annual reviews Opportunity to participate in Flo’s performance incentive scheme Paid holiday, sick leave, and female health leave Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents Accelerated professional growth through world-changing work and learning support In-person collaboration and work in a hybrid model, with 3 days per week spent in the office 5-week fully paid sabbatical at 5-year Floversary Flo Premium for friends & family, plus more health, pension and wellbeing perks Diversity, equity and inclusion Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities. Read our privacy notice for job applicants .