Architecture
In our previous posts, we broke down the individual components of production AI agents: how the tool-calling loop works, how system prompts govern behavior, how MCP connects agents to business systems, and how to configure extension points in practice. Each of those posts examined a single agent doing a single job.
This post is about what happens when one agent isn’t enough.
2025 was the year of single AI agents. 2026 is the year they start working together. The AI agent market is growing at 46% year over year, and Gartner projects that 40% of enterprise applications will feature task-specific AI agents by the end of this year — up from less than 5% in 2025. But Gartner also predicts that over 40% of agentic AI projects will be canceled by 2027, and the primary killers are cost overruns, coordination complexity, and inadequate governance.
In our previous posts, we broke down how system prompts govern agent behavior and how the tool-calling loop actually works. Both of those pieces assumed something that, in practice, is the hardest part of building a production AI agent: the agent can actually talk to your business systems.
That’s the integration problem. And until recently, it was brutal.
If you wanted an AI agent that could look up customer orders, check inventory, update a CRM record, and send a follow-up email, you needed four separate integrations — each with its own authentication flow, data format, error handling, and maintenance burden. Five AI platforms connecting to twenty business tools meant a hundred integration projects. Every new tool or model multiplied the work.
Most explanations of AI agents stop at “the LLM decides which tool to use.” That’s the easy part. The hard part is everything around it: how you define tools so the model actually picks the right one, how you handle failures mid-chain, and how you keep a stateless model acting like it has memory.
This post breaks down the core loop that powers every agent we build at Replyant.
The Agent Loop
Every AI agent, regardless of framework, runs the same fundamental cycle: