We're looking for an
AI Software Engineer
who wants to build autonomous AI systems with real business impact.
At Zentesimal, we build AI workers that don't just assist humans : they observe, reason, decide and act inside real Customer Success, Support and Revenue operations.
These systems run end-to-end, integrate deeply with existing tools, and are evaluated by measurable outcomes (including revenue).
This is an early-stage role with strong technical influence, direct exposure to real customers and production systems, and the potential to receive Phantom shares or equity. The role is part of our early engineering team.
What you'll work on
You'll work directly with the CTO and have real influence over architecture, system design and technical direction.
You'll design, build, deploy and continuously improve autonomous AI systems that :
Integrate deeply with existing business tools and workflows
Combine deterministic logic with LLM-based reasoning
Execute multi-step processes autonomously
Are observable, debuggable and evaluated like human teammates
This role combines backend engineering, hands-on experience with LLMs and agentic systems, and the ability to translate real customer needs into scalable AI architectures.
Responsibilities
Design and build agentic systems and multi-agent workflows
Model complex AI behavior using state machines and graph-based architectures
Combine deterministic logic with probabilistic LLM reasoning
Implement evaluation, feedback and learning loops for AI in production
Build platforms and interfaces that allow humans to communicate with AI workers, debug decisions, and evaluate outcomes
Develop API-based services and integrations (models, vendors, platforms)
Build ETL / ELT pipelines ensuring data quality and availability
You own the full lifecycle :
design → build → deploy → monitor → iterate
Required experience
You have :
~3+ years of backend engineering experience (TypeScript / Node.js preferred)
~3+ years working with relational databases (PostgreSQL preferred)
~ Proven experience shipping Generative AI systems to production, including LLM-based / agentic systems and embeddings and semantic search
~ Strong software design and architecture fundamentals
~ Experience in startup environments (builder mentality, comfort with ambiguity)
~ High autonomy, ownership and collaborative decision-making skills
~ Fluency in technical English
Especially valuable for this role
We strongly value experience or interest in :
State machines and explicit control flows (e.g. XState)
Graph-based agent architectures (e.g. LangGraph or similar)
Designing systems with explicit state, transitions and failure modes
Reasoning about long-running, multi-step autonomous processes
(Experience with orchestration tools like Inngest, Trigger.dev or Temporal is useful, but secondary to strong state and control modeling)
Bonus points
Vector databases and semantic retrieval systems
Serverless deployment experience
Interest or experience with Graph-RAG architectures
Basic familiarity with React / Next.js
What we offer
Opportunity to build cutting-edge AI systems with real revenue impact
High ownership and autonomy : ship fast, iterate faster
Competitive salary plus Phantom shares or equity arrangements for early team members
Flexible remote setup, with optional offices in Madrid and Barcelona
Small, highly technical team focused on quality, automation and execution
If you enjoy building AI systems that evolve, improve, and deliver real business value, we'd love to talk.
Software Engineering • Madrid, Spain