Growth Data Scientist

Viktor; Warszawa; On-site; PLN 180,000 - 300,000; Full time

Job summary

Viktor in Warsaw is seeking a quantitative modeling expert to predict customer lifetime value and guide acquisition, pricing and sales investment. You’ll connect retention, expansion and usage to LTV, test predictions, and present clear signals about uncertainty.

Work onsite with the growth, finance and data teams. You’ll build reproducible Python models and dashboards, backtest predictions, and communicate decisions to senior leaders. This is a hands-on role with ownership from day one.

Qualifications

• Strong statistical and quantitative modeling skills.
• Ability to validate models with backtesting and calibration.
• Experience with experimentation and causal inference.
• Advanced SQL and Python engineering skills.

Responsibilities

• Build and improve customer LTV models.
• Validate predictions before they drive decisions.
• Guide acquisition and pricing decisions with predicted LTV.
• Model attribution and incrementality across channels.
• Connect customer economics to financial planning and scenarios.
• Make models usable with reproducible code and dashboards.

Skills

Statistics

SQL

Python

Causal inference

Experimentation

Tools

ClickHouse

Hex

Python

PostHog

Stripe data

Job description

About Viktor

Viktor is the AI teammate. He lives in Slack and Microsoft Teams, connects to thousands of tools, and does real work for real companies: finance, marketing, ops, engineering. We're building the product that replaces half the SaaS stack.

The team is small. The scope is not.

The Short Version

You predict what customers will be worth over their lifetime, and use those predictions to guide acquisition, pricing and sales investment. This is a quantitative modeling role: you connect retention, expansion and product usage to customer lifetime value, test whether the predictions hold up, and make clear when they are too uncertain to act on.

You'll work onsite in Warsaw alongside Fryderyk, Matt, the growth team and finance, reporting to Fryderyk initially.

The Hard Part

Our customers haven't finished their lifetimes. Many cohorts are young, histories are incomplete, and some segments have little data. Meanwhile, new product surfaces change how customers use Viktor, expand and retain. A model that fits yesterday's customers may not predict tomorrow's.

You need to distinguish durable signals from noise, estimate value before a cohort matures, and show how much confidence a decision deserves. Backtesting, calibration and uncertainty are part of the work, not checks added at the end.

Attribution is another hard problem: a channel can appear to bring valuable customers without causing additional value. You'll separate attributed revenue from incremental impact, including the effect of sales activity, so we know where another dollar of investment is likely to pay back.

What You'll Actually Do

• Build and improve customer LTV models. Predict lifetime value from retention, expansion, usage and customer characteristics. Account for incomplete histories, young cohorts and sparse segments; revisit assumptions as customer behavior changes.

• Validate predictions before they drive decisions. Backtest on historical cohorts without leaking future information, check calibration and quantify uncertainty. Monitor model performance and define when evidence is too weak to act on.

• Guide acquisition and pricing. Turn predicted LTV, cost to serve and payback into recommendations on acquisition spend, customer segments and pricing. Make assumptions and trade-offs explicit.

• Model attribution and incrementality. Connect acquisition spend to customer lifetime value, quantify which channels bring valuable customers, and measure the incremental impact of marketing and sales activity. Use experiments and causal methods to guide budget allocation.

• Connect customer economics to financial planning. Use the customer models to inform growth, profit, runway and fundraising scenarios, with clear sensitivities rather than false precision.

• Make the models usable. Build tested, reproducible Python code and customer-lifecycle dashboards that explain the predictions, assumptions and uncertainty. By day 90, the team should have dashboards that help it understand the whole customer lifecycle.

• Work closely with growth, sales, finance and the Data Engineer. Own the modeling and interpretation; partner on reliable datasets and shared metric definitions rather than owning warehouse infrastructure.

Who You Are

• Strong statistical and quantitative modeling skills. You can reason about retention, expansion and lifetime value, choose appropriate methods, and explain their assumptions and limits.

• You know how to validate a model: backtesting, calibration, uncertainty estimation, leakage prevention and performance under changing customer behavior.

• Depth in experimentation and causal inference. You can distinguish correlation, attribution and incremental impact, and explain what the available data cannot establish.

• Advanced SQL and strong Python engineering skills. You can build, test and maintain reproducible modeling code, not just explore data in a notebook.

• Commercial judgment. You can turn a prediction into a defensible acquisition, pricing or sales-investment decision, including a recommendation not to act when evidence is weak.

• Agentic engineering is part of your daily workflow. You use coding agents to move faster while taking responsibility for the methods, code and conclusions.

• You work directly with decision-makers, challenge assumptions and follow through on whether your recommendations worked.

• Based in Warsaw or willing to relocate, working onsite with the team.

Why This Role Is Different

• You report to Fryderyk, our CEO, initially. Your mandate spans growth, sales and finance, rather than sitting inside one channel team.

• Customer LTV is the primary focus. Your models directly inform where we acquire customers, how we price and where we invest in sales.

• You work alongside the people making those decisions in Warsaw and see how the predictions perform in practice.

• Your models and metric definitions become part of a data layer used by people and AI.

Even Better If

• A background in quantitative research, statistics, econometrics or another field where predictions are rigorously tested against outcomes.

• Experience with customer lifetime value, survival or retention modeling, and SaaS or usage-based economics.

• Attribution, marketing-mix modeling or incrementality measurement on real marketing or sales investment.

• You've built something with LLMs that went beyond a demo.

Tech

ClickHouse, Hex, Python, PostHog, Stripe data.

How We Work

Small team, high trust, low process. Decisions are made by owners, not committees. You will ship your first week. You will talk to users your first day.

Why Viktor

We're building an AI teammate that does real work across a company's tools.

This is a rare window: everyone here owns something real. Not a task. A surface of the company that customers depend on.

That doesn't last forever. Right now, it's still true.

Compensation

Top-of-the-market salary and the kind of ownership that only exists at this stage.

This is an onsite role in Warsaw, working alongside the growth team and finance.