MTS: Senior Fullstack

Type: Full Time, Hybrid Team: Engineering Focus: Senior Fullstack

Who We Are We're a team of founders, engineers, researchers, creatives, and operators building what we believe will be one of the defining companies of the AI era. Some of us came from startups. Some from academia. Some from hospitality, defense, design, or completely different worlds. We don’t care how you got here - we care about your energy, intelligence, curiosity, resilience, and ambition.

Who We Are Not

• We are not remote. We value the spontaneous moments that happen when we’re together - over dinner, in the hallway, around whiteboards. We like being around each other because the best conversations here rarely happen in meetings.

• We are not your typical team. It’s not just the 10 countries we’re from, the languages we speak or our non-traditional backgrounds. We’re solving hard problems with people we respect - we make the most of our time together, we make it special.

• We are not another “polished” SF startup. We value velocity over speed, raw talent over brands, and genuine human connection above all else. We value being successful, not looking successful.

What You’ll Own & Build As a Member of Technical Staff within the Engineering Tribe, you won’t just be writing code - you’re building the product and the systems that turn simulated behavior into real product decisions. You’ll work across the stack, connecting complex backend systems (multi-agent simulations, evaluation pipelines) to frontend experiences that customers rely on to decide what to build next.

• Core Platform: Build and evolve the Seldon platform (Python) - the system customers use to design experiments, run simulations, explore behavioral outputs, and decide what to ship.

• Agent to Product Translation: Turn raw agent behavior into product functionality, bridging the gap between “what the system did” and “what the user should do next.” Strong application of agentic systems is the baseline.

• System Visibility & Trust: Build tooling that makes the system understandable and trustworthy.

• User Agency & Decisions: Help define how users interact with simulations and make decisions.

• Velocity & Ownership: Work in tight loops - ship fast, learn faster. Own features (backend → frontend → user impact), ship bi-weekly, and define best practices as we scale.

Who You Are

• End-to-End Systems Builder: You’ve invested 6+ years building production systems and understanding how data and logic flow from backend to frontend. You’re comfortable moving across the stack - and care deeply about how everything fits together.

• Product Engineer at Heart: You don’t build features - you build outcomes that help users make decisions. You know when to go deep, when to simplify, and when to ship to learn.

• AI-Native, User-Focused: You’re excited by LLMs, agents, and simulation systems - and you don’t just build for the tech, you build for the user. You translate complex behavior into insights.

• High Ownership, Low Ego: You take responsibility for outcomes, not just code. You surface problems early, adapt quickly, and prioritize being effective over being right.

• Comfortable at the Frontier: You thrive when the product isn’t in "maintenance mode.” You’re comfortable making decisions with incomplete information and building the playbook as you go.

• Uncomfortable with “It Just Works”: You crave the why, understand what worked or failed, and how to improve it. You drive clarity, debuggability, and elegant systems.

• All Backgrounds Welcome: Some of us are dropouts, some have PhDs. Some are tech veterans, some are first-timers. What matters - how you think, how you build, and how you work in teams.

• Bonus: Experience designing agentic systems or LLM-powered products, building internal tools or complex product workflows, and working in highly regulated environments.

Why Seldon

• The Timing: The entire product stack was designed for a world where building software was expensive. That world is gone. The next generation of companies will be built around understanding human behavior before anything goes live.

• The Team: A deeply ambitious, unusually diverse group of researchers, engineers, founders, and operators who care about building something meaningful together.

• The Problem: Deep science with real impact. We leverage behavioral modeling, cognitive science, and cutting-edge AI to solve real product challenges for real customers.

• The Traction: Real interest from some of the most sophisticated companies and organizations in product, research, finance, and government.

• The Backing: Backed by MaC VC, Protagonist, Weekend Fund and scouts at a16z, along with a team of MIT researchers and leaders from Discord, Airbnb, Meta, and Google.

• The Member Of Staff Philosophy: You don't care about titles — you value extreme ownership.

Comp & Benefits

• Salary: $180-200k base + equity

• Health (US only): 100% paid medical, dental & vision

• PTO: 28 days (inc 5 company-wide days on stats)

• Environment: Beautiful offices in SoMa & Tower Bridge optimized for deep collaboration

• WFH: 2 days/week (Mon & Fri) to catch up on laundry, save time commuting, and let your cat walk across the keyboard

• Adventures: Team dinners, offsites, and events throughout the year