Senior AI Developer

Santex is a US-based global company founded in 1999, with 25 years of experience in the software industry. Headquartered in California with offices in Córdoba, Argentina, its talent network spans over 18 countries thanks to its flexible, remote-first culture. Santex specializes in custom enterprise software development, operating through Hubs that include eCommerce, BIM, Mobility, Content Delivery, Integration, Web & Mobile Development, Cloud Computing, Artificial Intelligence (AI), Data Science, IT Consulting, and Services. The company is committed to making a positive impact across three dimensions: economic, social, and environmental.

Job Description: 

We are seeking Senior AI/ML Engineers to join a new, forward-thinking AI team, established in partnership with Santex in Mexico City. This team will focus on building enterprise production-ready AI solutions at scale, specifically driving innovation in the expense platform. The ideal candidates are technical operators with a strong backend platform focus who can drive innovation.

Responsibilities 

• Design, develop, and deploy AI-driven services and workflows ("agents") for the American Express expense platform.
• Focus on RAG (Retrieval-Augmented Generation) implementations, fine-tuning models, and building robust LLM workflows in production.
• Develop solutions for key features such as recommendations, predictions, chatbots for dashboard analytics, and smart receipt generation.
• Implement high standards for observability, testability, and metrics for all AI models and systems, addressing scrutiny on AI model decisions.
• Work in a collaborative, fast-paced environment to deliver enterprise-grade solutions.

Requirements 

• Senior-level experience in developing production-ready, scalable enterprise solutions.
• Strong proficiency in Golang (at least 5 years) in a backend engineer role. Prior non-AI-related Golang experience is acceptable.
• Strong applied experience with LLMs, RAG, fine-tuning, embeddings, and inference workloads.
• Hands-on experience building production AI systems (not only experimentation or prototypes).
• Strong knowledge of LLM mechanics, neural networks, prompting, embeddings, and evaluation.
• Deep understanding of the mechanics of LLMs, neural networks, training, fine-tuning, and AB testing/versioning models.
• Experience with cloud infrastructure and practical ML experience.

Soft Skills

• Strong professional working proficiency in English is required.
• Excellent English communication; prior experience working with US-based teams is a a strong plus.
• Strong ownership and autonomous execution.
• Ability to work in fast-paced, ambiguous environments.
• Team-first mindset with a focus on collaboration and communication.
• “Technical operator” mentality—able to design, build, and run production systems end-to-end.

Desirable

• React experience (a huge plus, especially for the Full-Stack profile).
• Focused experience in one of the following domains to balance the team:
  • Backend Platform Engineer: Highly focused on cloud infrastructure and robust ML/system scaling.
  • Data Science/ML Engineer: Strong focus on model development, fine-tuning, and AI workflow creation.
  • Full-Stack Engineer: Strong backend skills (Golang/Typescript) with hands-on experience in React.

Required Location

México City: 1 or 2 times a month in-office presence.