Sr Full Stack Engineer

Colossus Technologies Group; New York (NY); On-site; USD 140,000 - 190,000; Full time

Job summary

Colossus Technologies Group is seeking a Senior Full Stack Engineer for an AI Platform in New York. You’ll join an early-stage, well-funded team to shape architecture, build across the stack, and develop production AI agents and agentic workflows.

You'll design and implement systems with React, Python, .NET, and PostgreSQL, own features end-to-end, and build LLM-based agents and workflows. This role emphasizes ownership, scalability, and close collaboration with product and design.

Qualifications

• Strong full-stack engineering and architecture experience.
• Hands-on experience with React and backend development.
• Experience building with LLMs and generative AI.
• Understanding of prompt design, RAG, context management, evaluation, and tool use.
• Ideally, experience with agent frameworks such as LangGraph, OpenAI Agents SDK, Claude Agent SDK, Pydantic AI, or similar.
• Comfortable working in an early-stage environment with significant ownership.

Responsibilities

• Design and build scalable full-stack systems across React, Python, .NET, and PostgreSQL.
• Own features and architecture end-to-end.
• Build LLM-based agents and agentic workflows.
• Integrate LLMs, RAG, tool use, and orchestration into production applications.

Skills

React

Python

.NET

PostgreSQL

LLMs

RAG

Agent frameworks

Tool integration

Tools

LangGraph

OpenAI Agents SDK

Claude Agent SDK

Pydantic AI

Job description

Senior Full Stack Engineer – AI Platform

We’re hiring a Senior Full Stack Engineer to join an early-stage, well-funded team building a greenfield, AI-native platform. This is a high-ownership role where you’ll help shape the architecture, build across the stack, and develop production AI agents and agentic workflows

.What You’ll D

• oDesign and build systems across React, Python, .NET, and PostgreSQ
• LOwn features and architecture end-to-en
• dBuild LLM-based agents and agentic workflow
• sIntegrate LLMs, RAG, tool use, and orchestration into production application
• sHelp establish engineering standards around scalability, testing, and maintainabilit
• yPartner closely with product and design to influence what gets buil

tWhat We’re Looking Fo

• rStrong full-stack engineering and architecture experienc
• eHands-on experience with React and backend developmen
• tExperience building with LLMs and generative A
• IUnderstanding of prompt design, RAG, context management, evaluation, and tool us
• eIdeally, experience with agent frameworks such as LangGraph, OpenAI Agents SDK, Claude Agent SDK, Pydantic AI, or simila
• rComfortable working in an early-stage environment with significant ownershi