Staff Software Engineer — AI Messaging & RCS Platform

21X (formerly Structurely) is hiring a Staff / Principal Software Engineer to lead the architecture and development of its AI-powered RCS messaging platform. The role owns scalable messaging infrastructure, integrations with conversational AI and enterprise systems, and technical direction for the platform.

Responsibilities:

• Architect and develop a scalable, multi-tenant RCS messaging platform supporting enterprise customers
• Build integrations with RCS Business Messaging providers such as Vonage, Google RBM, and other messaging partners
• Develop infrastructure for branded RCS agents, rich cards, carousels, suggested replies, media, and interactive messaging experiences
• Manage message routing, delivery status, carrier interoperability, capability detection, and SMS fallback
• Design reliable messaging pipelines supporting high-volume inbound and outbound communication
• Build APIs, webhooks, event processing, message queuing, and asynchronous workflows
• Establish platform reliability, security, observability, and performance standards
• Integrate RCS messaging with 21X’s existing AI agent orchestration infrastructure
• Enable AI agents to maintain conversational context, reason through customer requests, and execute business actions
• Develop integrations supporting LLMs, function calling, agent tools, and external APIs
• Support multimodal and interactive conversational experiences, including rich media and structured user interactions
• Enable seamless continuity between RCS, SMS, voice, email, and other communication channels
• Collaborate with our AI engineering team to improve agent performance, reliability, and conversational experiences
• Build messaging workflows that support product discovery, customer engagement, sales, service, and commerce
• Enable AI agents to recommend products, display interactive product catalogs, capture customer selections, and facilitate secure checkout experiences
• Integrate with CRM platforms, ticketing systems, commerce platforms, payment providers, scheduling systems, and enterprise APIs
• Develop infrastructure supporting large-scale outbound campaigns, automated follow-ups, and inbound customer engagement
• Build tools for message templates, conversation analytics, engagement reporting, and conversion attribution
• Implement appropriate consent, opt-out, privacy, and messaging compliance controls
• Own the technical architecture, engineering decisions, and long-term evolution of our messaging platform
• Design scalable, fault-tolerant distributed systems capable of supporting millions of customer interactions
• Establish engineering best practices around testing, deployment, monitoring, security, and performance
• Work closely with product leadership and executive management to translate business opportunities into technical capabilities
• Mentor engineers and provide technical direction across backend, frontend, and AI engineering teams
• Help establish the foundation for a dedicated messaging engineering organization as the platform scales

Requirements:

• 7+ years of professional software engineering experience, including significant backend and distributed systems development
• Demonstrated experience architecting and building production-grade, high-scale software platforms
• Strong proficiency in one or more backend languages such as TypeScript/Node.js, Go, Java, or Python
• Deep understanding of APIs, webhooks, event-driven architecture, message queues, asynchronous processing, and distributed systems
• Experience with cloud-native infrastructure, preferably AWS
• Experience building or integrating communication systems, messaging platforms, or real-time applications
• Familiarity with LLM APIs, conversational AI, agent orchestration, or tool-calling architectures
• Strong understanding of system reliability, security, observability, and performance optimization
• Ability to independently own complex technical projects from architecture through production
• Excellent technical communication skills and the ability to collaborate across engineering and business teams
• Direct experience with RCS Business Messaging (RBM), SMS, or CPaaS platforms
• Experience working with Vonage, Twilio, Infobip, Sinch, Google RBM, or similar communications infrastructure
• Experience developing conversational AI agents using OpenAI or other leading language models
• Experience with multi-tenant SaaS platforms, high-throughput messaging systems, or enterprise communications infrastructure
• Experience with real-time commerce, payments, CRM integrations, or workflow automation
• Previous experience as a Staff Engineer, Principal Engineer, Tech Lead, or founding engineer