Senior Software Engineer, Core Open-Source- Weights & Biases

About the position At marimo, we’re on a mission to make the world’s best open-source programming environment for working with data, together with a world-class, scalable, and performant cloud-hosted counterpart. marimo is a reinvention of the Python notebook — it feels like a next-gen reactive Python notebook, but is stored as pure Python that can be versioned with Git, deployed as a data app, run as a script, and reused as a module. Incubated initially with scientists at Stanford, marimo is now used by leading companies, labs, and universities around the world, with millions of downloads since launch and over 17,000 stars on our GitHub repository. On the marimo team, we believe that the tools we use shape the way we think — better tools, for better minds. If you're passionate about developer tools, thrive in ambiguity, enjoy solving challenging engineering problems at scale, and yearn for greenfield problems, you'll fit right in. As a senior software engineer on marimo's core open source team, you’ll take ownership of projects across marimo's open-source ecosystem, focusing on marimo's backend and its Python ecosystem. You will influence critical decisions on library design, making sure our APIs remain simple yet composable; you'll also design new capabilities that push the boundaries of interactive computing without complicating the user experience. You'll work in the open, at a fast pace — engaging promptly and empathetically with a large and vocal community of users and contributors, triaging their issues and reading between the lines to understand their unstated needs. All the while, you'll exercise judgment to balance the needs of our community with our own roadmap and vision.

Requirements

• 4+ years of experience in software engineering
• Proficiency in Python, with strong fundamentals that are language agnostic
• Proficiency in computer systems, including parallel computing (threading, multiprocessing), concurrency (asynchronous programming), basic networking/inter-process communication
• Experience in library design and/or open-source development
• Strong communication skills, written and verbal

Nice-to-haves

• A passion for and experience building developer tools, especially for AI, ML, or data
• A passion for working with data, with the ability to empathize with practitioners and researchers in AI, ML, data engineering, NLP, or other quantitative work
• An eye for visual and interaction design, with an emphasis on simplicity
• You find enjoyment in connecting with users and community daily
• Proficiency in Typescript, or a willingness to learn
• Experience with AI engineering, including MCP and agents
• Experience with SQL, databases, and data engineering
• Experience with at least one systems language, such as C or Rust

Benefits

• Medical, dental, and vision insurance - 100% paid for by CoreWeave
• Company-paid Life Insurance
• Voluntary supplemental life insurance
• Short and long-term disability insurance
• Flexible Spending Account
• Health Savings Account
• Tuition Reimbursement
• Ability to Participate in Employee Stock Purchase Program (ESPP)
• Mental Wellness Benefits through Spring Health
• Family-Forming support provided by Carrot
• Paid Parental Leave
• Flexible, full-service childcare support with Kinside
• 401(k) with a generous employer match
• Flexible PTO
• Catered lunch each day in our office and data center locations
• A casual work environment
• A work culture focused on innovative disruption

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