The best stack for the AI Era

Will Cromwell argues that Elixir and the Phoenix framework are the optimal tech stack for building AI-integrated applications, citing their ability to handle massive concurrency with minimal infrastructure, streamline text streaming via Phoenix LiveView, and offer ecosystem stability compared to Node.js.

Back to blog /blog/ Why Elixir and Phoenix are the Best Stack for the AI Era Discover why Elixir and Phoenix are the ultimate tech stack for the AI era, offering massive concurrency, effortless text streaming, and rapid iteration. Will Cromwell 7 min read If you’ve spent the last year building AI-integrated applications, you’ve probably noticed a recurring architectural nightmare. We are constantly waiting on network calls. We are juggling thousands of persistent WebSocket connections to stream tokens back to impatient users. And to handle all of this, we are bolting complex asynchronous queues, Redis instances, and bloated frontend frameworks onto our traditional MVC or microservice backends. We’re trying to build next-generation, highly concurrent AI applications using tools designed for the stateless request/response web of 2014. After years of architecting systems at scale, I’ve realized that the most pragmatic choice for building in the generative AI era isn’t the stack you might expect. It’s Elixir and the Phoenix framework. 1. Massive Concurrency with a Microscopic Footprint When building AI wrappers, agents, or multi-user chat interfaces, your application is inherently I/O bound. You are spending most of your time waiting for an LLM provider’s API to respond. In traditional environments like Ruby, Python, or Node.js, holding open thousands of connections while waiting for an external API requires serious infrastructure gymnastics — event loops, worker pools, and memory bloat. Elixir runs on the Erlang VM BEAM , which was literally invented by telecom engineers to handle millions of concurrent phone calls without dropping a sweat. In Elixir, every user connection, every background task, and every LLM API call runs in its own lightweight process. These aren’t OS-level threads; they take up literal kilobytes of memory. You can easily manage tens of thousands of concurrent users chatting with AI agents on a single, cheap server. No Kubernetes clusters required. No complex autoscaling rules just to handle a traffic spike. The system simply absorbs the concurrency natively, leaving a remarkably small infrastructure footprint. 2. The Ideal Engine for Streaming Text The “ChatGPT effect” has permanently changed user expectations. You cannot make a user wait 15 seconds for a complete response; you have to stream the output token-by-token. In a standard stack, this is surprisingly hard to get right. You need a frontend framework React/Vue managing complex state, a WebSocket server handling the streams, and a message broker like Redis keeping everything in sync across your backend containers. It’s a distributed systems headache just to put words on a screen. Enter Phoenix LiveView . LiveView keeps the state on the server and pushes HTML updates directly to the client over a single, multiplexed WebSocket. When your backend receives a new text token from the OpenAI API, you simply update the server-side state. Phoenix automatically diffs the UI and pushes just the new token across the wire to the browser. No frontend state management. No separate GraphQL API. No message brokers. Because Phoenix has distributed PubSub built directly into the framework, broadcasting AI-generated streams to one user — or ten thousand users in a shared collaborative room — is functionally a one-liner. 3. Ecosystem Sanity: Elixir vs. the Node.js Moving Target When you build a fast-moving AI startup, the last thing you want to spend time on is fighting your own tools. Look at the Node.js ecosystem right now. It is in a perpetual state of identity crisis. You have to choose between Node, Deno, or Bun. You have to figure out if your libraries support CommonJS or ESM. You have to stitch together a meta-framework like Next.js with an ORM, a WebSocket library, and a background worker queue, hoping they all play nice after the next major npm upgrade . It’s an exhausting treadmill of breaking changes and fragmented community standards. Elixir offers absolute architectural sanity by comparison. The core tooling in Elixir is remarkably mature and stable. Phoenix isn’t just a router; it’s a cohesive, battery-included framework that has evolved predictably for a decade. Data persistence is handled by Ecto, a robust database wrapper that doesn’t suffer from the object-relational impedance mismatch of JavaScript ORMs. Because Elixir is built on the BEAM, features that require third-party infrastructure in the Node world — like background job processing via Oban or pub/sub messaging — run directly inside the application memory pool. You get a single, rock-solid ecosystem where code written five years ago still compiles and runs flawlessly today. You can focus 100% of your energy on shipping AI features, rather than refactoring build tools and managing dependency hell. 4. Iterating at “AI Speed”: The Case for the Monolith The generative AI landscape is shifting underneath our feet on a weekly basis. New foundation models drop constantly, user expectations are evolving at lightspeed, and what looked like a solid product idea on Monday might be rendered obsolete by an OpenAI or Anthropic update on Thursday. In this hyper-volatile environment, finding Product-Market Fit PMF is a brutal race. It’s not about slowly optimizing a stable feature set; it’s about radical, rapid experimentation. You might need to completely rip out a RAG pipeline, pivot your entire core use case, and fundamentally alter your database schema — all in the same week. If your startup is built on a complex web of microservices, this kind of agility is mathematically impossible. You cannot afford to coordinate a schema change in a database service, a prompt update in a Python AI worker, and a UI overhaul in a React frontend across three different repositories and CI/CD pipelines just to test a new hypothesis. Microservices optimize for massive, specialized engineering teams, but they absolutely slaughter your iteration speed when you are still searching for PMF. Phoenix encourages the monolith, bringing your entire stack into a single codebase. Need to drastically change how an AI agent stores conversational memory and immediately stream that new format to the user? You make the change in one place, open one pull request, and deploy one artifact. But unlike the tangled spaghetti codebases of the past, Elixir provides built-in tools like Contexts to enforce strict, logical boundaries between your domains. You get the agility to pivot your product overnight to match the shifting AI market, along with the architectural soundness to scale it once you actually strike gold. 5. The Secret Weapon: AI Writes Better Elixir This is the point that usually raises eyebrows. Isn’t Python the language of AI? For training models and running data science pipelines, absolutely. But for building robust web applications using those models, Elixir holds a massive advantage: Large Language Models are exceptionally good at writing it. This isn’t just an anecdotal observation; it’s backed by rigorous benchmarking. In late 2025, Tencent’s AI team published the AutoCodeBench study https://autocodebench.github.io/ , a large-scale benchmark comprising nearly 4,000 real-world programming problems across 20 languages. The results were staggering: Elixir scored the highest completion rate of any language tested. When combining the output of over 30 evaluated models, 97.5% of Elixir problems were solved by at least one model. Even looking at individual model performance, Elixir reigned supreme. Claude Opus 4, for example, achieved an 80.3% success rate on Elixir tasks — its highest score overall, decisively beating languages with vastly more training data like C 74.9% and Kotlin 72.5% . How does a language with a fraction of Python’s market share perform so much better? It comes down to architecture: Immutability enables local reasoning: LLMs struggle profoundly with hidden state, complex object-oriented inheritance trees, and unpredictable side effects. In Elixir, data is immutable. The AI doesn’t have to guess if a function mutates an object five layers deep; it simply takes data in and returns data out. Explicit Data Flow: The pipe operator | forces a clean, linear transformation of data from top to bottom. It’s highly predictable for an LLM to generate and extend. Pattern Matching over Defensive Coding: Instead of writing dozens of nested if/else checks that easily confuse coding agents, Elixir relies on strict pattern matching to handle both “success” and “error” tuples cleanly. When you ask Claude or GPT-4 to write an Elixir module, the fundamental rules of the language force the AI to produce clean, decoupled, and predictable code. Because the boundaries are so explicit and the mix format styling is universal, AI-generated Elixir code works on the first try far more often than in any other language I’ve used in my career. The Takeaway The AI boom is rewarding teams that can ship highly interactive, real-time applications quickly. If you are bogging your team down in managing connection pools, debugging React rendering cycles for streaming text, coordinating microservice deployments, and scaling up cloud infrastructure just to handle idle WebSocket connections, you are wasting cycles on the wrong problems. Elixir and Phoenix give you the concurrent power of a telecom switch, the real-time interactivity of a complex SPA, the rapid iteration speed required to find PMF in a volatile market, and a functional paradigm that pairs beautifully with AI coding assistants. It is, without a doubt, the unfair advantage of the modern web.