645 Ventures is looking for a SeniorFull-Stack Data Scientist who can maintain  and extend a live, production-grade system while also building data pipelines and ML driven scoring systems. 

This role is designed for someone comfortable operating real systems with real users. You  will own features end-to-end across our Ruby on Rails + React monorepo, from database  and backend logic through frontend workflows and deployed ML models. 

Key Responsibilities:

• Maintain and evolve a live production platform 

• Own backend services, APIs, and frontend components within a Rails + React monorepo 

• Design, build, and maintain scalable data pipelines 

• Develop, deploy, and monitor ML-based scoring and ranking systems - ensure system reliability, observability, and data quality 

• Collaborate closely with product, research, and design

Core Technical Stack at 645:

• Ruby — Ruby on Rails backend

• JavaScript / JSX — React frontend components 

• SQL — PostgreSQL (schema design, performance tuning, analytics)

• Python (polars, duckdb, etc) 

• AWS 

• Agentic software development

• Bash for development and automation scripts

• Docker — local development and deployment environments 

• Webpack / Babel — frontend build and configuration 

• Familiarity with ML deployment, feature engineering, or model monitoring 

• Claude Code, Codex, or Cursor

The core stack is Ruby on Rails + React.

Qualifications:

• Ownership mindset — you build it, you run it 

• Strong Technical Engineering or Data Science Background: 7+ years experience across software engineering, data engineering, or data science

• Live Production Execution: Proven experience maintaining live production systems 

• Technical Rigor: Strong backend instincts with full-stack fluency 

• Applied ML Experience: Practical, applied ML experience (not research-only) 

• Analytical Skills: Comfort working with messy, real-world data. Desire to learn or understands the VC-oriented analytics and metrics.

• Communication & Synthesis: Ability to translate complex technical concepts into concise, actionable insights for a team of investors. Experienced working with end-users.

Examples of Projects You Could Work On:

• Maintaining and extending a live system used for internal decision-making

• Designing cost-efficient data ingestion pipelines pulling from third-party APIs and internal sources 

• Upfront product work, such as documenting product requirements, writing user stories, collecting feedback and testing MVPs 

• Building and iterating on an ML-based scoring model used to rank or prioritize entities 

• Improving frontend workflows for reviewing, debugging, and explaining scores to users 

• Hardening production systems: monitoring, alerting, performance tuning, and reliability  improvements 

• Ad hoc data queries and projects

About 645 Ventures

645 Ventures is a venture capital firm that partners with exceptional founders building iconic companies. The firm invests at the Pre-Seed, Seed, Series A, and growth stages across fintech, consumer, healthtech, enterprise, cybersecurity, infrastructure/developer tools and deep tech. 645 Ventures supports founders through its resource-intensive approach encompassing hiring, customer introductions and growth strategy, leveraging its proprietary software platform Voyager and deep Connected Network. 645 Ventures manages over $550M in AUM across five funds with investments in industry leaders including Goldbelly, Iterable, Overtime, Resident (acq. By Ashley Home, Inc.), Setpoint, ShopCircle and Shift5. Learn more at www.645ventures.com.