Senior Backend / Full-Stack Engineer (Founding Team)

Karma | London, United Kingdom | 1mo ago

This role has closed. Here are similar open builder roles:

1.	Marketing Productivity Engineer (Sigma Computing) San Francisco, United States+2 \| $130,000 – $165,000/yr \| on-site \| full-time \| senior \| performance marketing, growth engineering, marketing operations \| 1mo ago
2.	Software Engineer, Agents (Decagon) London, United Kingdom \| £125,000 – £180,000/yr \| on-site \| full-time \| mid \| python, typescript, asynchronous programming \| 1mo ago
3.	Founding / Software Engineer (Atarus) London, United Kingdom \| on-site \| full-time \| lead \| python, typescript, cloud infrastructure \| 2mo ago
4.	Staff ML Research Engineer \| LLM Fine-Tuning \| RL \| SFT \| DPO (Optimal) London, United Kingdom \| £210,000 – £305,000/yr \| on-site \| full-time \| senior \| llm fine-tuning, reinforcement learning, sft \| 2mo ago
5.	Staff AI Engineer (SR2 \| Socially Responsible Recruitment \| Certified B Corporation™) London, Greater London, United Kingdom \| on-site \| full-time \| senior \| ai engineering, llm, agentic ai \| 2mo ago
6.	AI Engineer (trg.recruitment) London, London, United Kingdom \| From £200,000/yr \| on-site \| full-time \| mid \| python, typescript, react \| 2mo ago
7.	Founding Engineer (Letty) London, London, United Kingdom \| £80,000 – £120,000/yr \| on-site \| full-time \| lead \| python, fastapi, backend fundamentals \| 2mo ago
8.	AI Product Design Engineer (Engine AI) London, London, United Kingdom \| on-site \| full-time \| entry \| react, typescript, product design \| 2mo ago

browse all open builder jobs →

Original posting (closed) below

£75,000 – £100,000/yr| full-time | on-site | senior | 2+ years

skills: python, go, node.js, api design, microservices, data modelling, event-driven architectures, real-time systems, aws, gcp, ad-serving infrastructure, partner apis, rewards systems, loyalty systems, full-stack development, backend development

We're a small London team, 2+ years in, building a real-time consumer platform powered by AI in a category that doesn't exist yet, going after a problem worth solving. Free for users, brand-funded on the commercial side. Working iOS prototype, validated UX, advisory board across enterprise tech and behavioural science, alpha launches lined up for later in 2026.

The founding tech team is already in place across iOS, Flutter, AI/ML, and product design, with backgrounds across agentic AI, consumer fintech, and mobile at scale. The seat we're hiring for is the founding backend / full-stack engineer who'll own the architecture. APIs, data layer, real-time systems, cloud infrastructure. You'll design it from scratch alongside the rest of the team, built for consumer scale from day one.

What we're looking for:

- Built and scaled backends for consumer products under real load. Social, marketplace, or community experience a strong plus.

- Fluent in Python, Go, Node, or similar. Strong opinions on API design, microservices, and data modelling.

- Comfortable with event-driven architectures, real-time systems, and AWS or GCP at production scale.

- Bonus: ad-serving infrastructure, partner APIs, rewards/loyalty systems.

- UK-based already (no net-new visa sponsorship for this role), with us in our London office most days. We're a small team that works best in the room together.

We're vague on the concept for stealth reasons. Happy to take you through our prototype on a call.

Email careers@karmapt.com and mention Hacker News in your note. I'll come back quickly.

Benefits

equity · health insurance

Get new builder jobs daily: