Sofia-based I Senior Product Engineer (Python)

About Infinite Lambda

Infinite Lambda is Europe’s fastest-growing data and AI consultancy. We empower leading companies to scale and become data-first through agile, cloud-native solutions and cutting-edge practices.

Our mission is to bring top professionals together to make an impact at the intersection of tech and sustainable growth.

Headquartered in London and having distributed teams based in the UK, France, Hungary, Slovakia, Bulgaria, Vietnam, Singapore, Italy, Romania and now expanding to South America we embrace diversity and make sure everyone is happy to be their true self at work. We have already started building teams in Brazil, Argentina, and Chile, and are looking forward to welcoming more teammates to contribute to meaningful projects. Together, we can grow, learn, and experiment with the cutting-edge data and AI technology (dbt and Snowflake among others) that we are all excited about.

About the role

We are hiring a Senior Product Engineer to own a subsystem of Flowline , our platform for migrating legacy ETL estates to dbt, Fivetran and cloud data warehouses.

Mission: Own a Flowline subsystem from spec to production, keep its quality high as agents write more of the code, and help associates grow into the same role.

Reports to : CPO

Anticipated start date: Jan 2027 onward

Location : Sofia (Bulgaria), hybrid

Interview process

Intro call (with TABP): 45-min

Take-home exercise: up to 4 hours to complete

Technical interview (with Product team): 90-min

Cultural chat (with Executive member): 45-min

What You’ll Do

Owns a subsystem of Flowline end to end, for example a source-vendor extractor, the BI conversion path, or the IDE extension. Accountable for its correctness on client estates.

Writes the specs for their subsystem and for cross-cutting features, with acceptance criteria. The Founding Architect reviews changes to the conversion contract and the architecture.

Runs several agents in parallel and asynchronously on their subsystem. Writes and maintains the skills, rules and eval cases those agents depend on.

Reviews agent-authored and associate PRs in their area. Rejects code that drifts from spec or that the author cannot explain.

Supports Infinite Lambda delivery teams on live migrations. Triages conversion defects raised at UAT, fixes the root cause in the converter, and updates the runbook.

Mentors associate engineers on spec writing, code review and modernisation patterns, and takes part in hiring.

Expectations and KPIs

Subsystem correctness: conversion defects in their subsystem found at client UAT per 1,000 converted objects, falling quarter on quarter.

Change failure rate across the subsystem, including agent and associate changes they approved.

Review escape rate: defects that reach UAT through PRs they reviewed.

Spec stability: % of their specs implemented without amendment once the build starts.

Delivery support: time from a delivery team raising a conversion defect to a fix being merged.

Associate progress: associates they mentor meet the 12-month growth gate.

Requirements

Experience: 5+ years of software engineering, including end-to-end ownership of a production component. We assess level on demonstrated scope, so treat years as a guide.

Agentic tooling: Daily, fluent use of Claude Code, Cursor or equivalent, including running agents asynchronously and writing the rules, skills and tests that keep their output correct.

Engineering: Strong Python and comfortable across the stack. Able to design a component, choose a testing strategy and diagnose performance problems.

Data and ETL: Working knowledge of at least one legacy ETL tool (Informatica PowerCenter, SSIS, Talend or IICS) and of dbt on a cloud warehouse. Able to reason about slowly changing dimensions, incremental loads, grain and null handling.

Spec-driven development: Has written specs that other engineers or agents implemented against.

Communication: Clear written English. Comfortable working directly with delivery teams and client engineers.

Education: A degree in Computer Science, Engineering or a related field is preferred, or equivalent practical experience.

The following soft skills are highly appreciated:

You are a self-starter and set your own priorities within the team's plan.

You are comfortable working in a distributed team.

You enjoy helping less experienced engineers improve their work.

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Promotion gate from Associate

An Associate moves to Senior when all of the following hold:

Authors a subsystem spec signed off by the Founding Architect.

Owns that subsystem in production for a quarter with change failure rate within target.

Reviews other engineers' and agents' PRs, with review escape rate within target.

Why join Infinite Lambda

We support your growth with dedicated learning time, access to top-notch resources and a knowledge-sharing culture;

You work autonomously here in a wholesome environment and get as much paid holiday as you need;

The projects are diverse and give you plenty of opportunity to experiment with new tech;

The benefits are plenty , with work-from-home budget, a company MacBook and more on the list.

▶ ▶ Submit your CV in English in PDF .

▶ ▶ Mind that as we are an international team, internal communication is in English.

▶ ▶ To ensure legislative compliance, applicants may be asked to provide up-to-date proof of a clean criminal record. Examples of said proof include extract n°3 of the Criminal Record (France), Büntetlen előélet (Hungary), Disclosure and Barring Service (DBS) check (UK), an extract from the Criminal Register (Slovakia), or a country-specific equivalent. Providing proof of a clean criminal record is the final step in the hiring process and will only be requested should the applicant accept an offer from Infinite Lambda.

Infinite Lambda is an equal opportunity employer. Our inclusive culture celebrates diversity and treats everyone with dignity and respect. Accordingly, our selection process will never discriminate against applicants on the grounds of any characteristics, such as disability, age, gender, sexual orientation, family status, race, faith or other.