AI Software Engineer - Early Team

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., * 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

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

• 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.