RelayPlane vs Vercel AI SDK
The Vercel AI SDK is a best-in-class TypeScript library for building streaming AI interfaces. RelayPlane is an npm-native cost-intelligence proxy that governs spend and routes traffic. They solve different problems and work well together.
TL;DR
Choose RelayPlane if you want:
- Per-request USD cost tracking on every live LLM call
- Smart routing: cheaper models for simple tasks, capable models for complex ones
- Per-agent cost attribution and runaway loop detection
- Zero code changes: point any OpenAI-compatible tool at localhost:4100
- Budget enforcement and spend alerts across your entire agent fleet
Choose Vercel AI SDK if you need:
- Streaming chat and completion UIs with useChat and useCompletion hooks
- Typed provider adapters for OpenAI, Anthropic, Google, and Mistral
- Deep Next.js integration with Server Actions and App Router streaming
- A free, MIT-licensed library with no infrastructure to run
Feature Comparison
| Feature | RelayPlane | Vercel AI SDK |
|---|---|---|
| Primary purpose RelayPlane sits in the live API call path as a localhost proxy. Every LLM request flows through it so costs, latency, and routing decisions are tracked automatically. The Vercel AI SDK is a client and server library for building streaming chat interfaces and AI features in Next.js and other React frameworks. | LLM routing proxy with cost intelligence | TypeScript streaming library for AI-powered UIs |
| Sits in the live API call path RelayPlane is a localhost proxy on port 4100. Every LLM request your agent or app makes is routed through it before reaching the upstream provider. The Vercel AI SDK calls providers directly from your server-side code and does not intercept traffic through a proxy. | ||
| Installation method RelayPlane is a global CLI binary that runs as a background proxy. The Vercel AI SDK is a library imported directly into your application code. Both are npm packages but they serve fundamentally different roles in the stack. | npm install -g @relayplane/proxy | npm install ai |
| Setup time RelayPlane starts with a single command and proxies traffic immediately with no code changes required. The Vercel AI SDK requires installing the package, configuring provider API keys, and integrating useChat or useCompletion hooks into your UI components. | ~30 seconds | ~5 minutes (install + provider keys + UI wiring) |
| Streaming UI support The Vercel AI SDK is purpose-built for streaming. It provides useChat, useCompletion, and useObject hooks that stream tokens to the browser in real time and handle partial state updates gracefully. RelayPlane is a proxy layer focused on cost governance and routing, not on building streaming chat interfaces. | ||
| Provider abstraction (OpenAI, Anthropic, Google) The Vercel AI SDK ships first-class provider adapters for OpenAI, Anthropic, Google, Mistral, and others. You switch providers by swapping the adapter. RelayPlane proxies OpenAI-compatible traffic and normalizes requests but does not provide typed SDK methods for each provider. | Via OpenAI-compatible base URL | |
| Per-request USD cost tracking RelayPlane computes exact USD cost per request using live pricing tables and stores results locally in SQLite. The Vercel AI SDK returns token counts in the response metadata but does not calculate or display dollar costs, aggregate spend, or alert on budget thresholds. | ||
| Cost dashboard RelayPlane provides a local dashboard showing spend by model, agent, and time period. The Vercel AI SDK is a library with no companion dashboard. Cost visibility requires building your own logging layer on top of it. | ||
| Smart model routing RelayPlane routes requests dynamically: simple tasks are sent to cheaper models, complex tasks to more capable ones. The Vercel AI SDK does not route between models automatically. You pick the model in code and it calls that model every time. | Cost-optimized routing by task complexity | |
| Per-agent cost attribution RelayPlane fingerprints system prompts to attribute cost and usage to individual agents. You can see exactly which agent is driving which spend. The Vercel AI SDK has no concept of agent attribution or cost grouping. | ||
| Runaway loop detection RelayPlane detects agents caught in repetitive loops and can stop them before costs spiral. The Vercel AI SDK does not monitor for runaway request patterns because it does not sit in the call path observing traffic over time. | ||
| Token limit enforcement RelayPlane enforces token budget policies globally across all requests from all agents. The Vercel AI SDK accepts a maxTokens parameter per individual call, but there is no global policy layer or cumulative budget enforcement. | maxTokens parameter per call | |
| Works without code changes RelayPlane is a drop-in proxy. Point any OpenAI-compatible tool at localhost:4100 and cost tracking begins with zero code changes. The Vercel AI SDK is a library that must be imported and integrated into application code. | ||
| Works with Claude Code, Cursor, and AI coding tools RelayPlane works with any OpenAI-compatible client by acting as a transparent proxy. Claude Code, Cursor, and similar coding tools can route through it immediately. The Vercel AI SDK is designed for building applications, not for instrumenting third-party AI tooling. | ||
| Latency tracking (p50 / p95) RelayPlane tracks p50/p95 latency per model and provider across all requests over time. The Vercel AI SDK returns duration in the usage metadata for each individual call but does not aggregate latency statistics across calls. | Duration in response metadata only | |
| Local-first / no cloud required RelayPlane stores all cost and latency data in local SQLite by default. No request data leaves your machine unless you enable cloud sync. The Vercel AI SDK is a library that calls provider APIs directly, so your prompts and completions travel to those upstream services. | Library runs locally; data goes to provider APIs | |
| Framework focus The Vercel AI SDK has the deepest integration with Next.js, including Server Actions and App Router streaming patterns. RelayPlane works in any Node.js environment: scripts, agents, CLIs, or web servers, regardless of framework. | Any Node.js or TypeScript environment | Next.js and React (also works with other frameworks) |
| Pricing The Vercel AI SDK is a free, open-source MIT library. RelayPlane has a free tier for local cost tracking and paid plans that unlock team dashboards, budget alerts, and policy enforcement. | Free tier + paid plans from $9/month | Free and open source (MIT) |
How RelayPlane Fits Into Your Stack
Cost governance that the Vercel AI SDK was never designed to provide
The Vercel AI SDK solves a real problem: building polished streaming chat UIs in React with minimal boilerplate. It does that extremely well. But it was not designed to answer the question your finance team will eventually ask: how much did this feature cost last month, and which model was responsible? RelayPlane was built specifically to answer that question. It tracks every request, attributes cost to the agent or feature that generated it, and alerts you when spend exceeds a threshold.
A proxy layer that instruments everything without touching your code
When you use the Vercel AI SDK, cost tracking requires adding custom logging to every route handler or server action that calls a model. With RelayPlane, you point your provider calls at localhost:4100 and every request is tracked automatically. You get cost history, latency percentiles, and model usage breakdowns without writing a single additional line of logging code.
Smart routing that the Vercel AI SDK leaves to you
The Vercel AI SDK gives you a clean way to call whichever model you choose. Choosing which model is your problem. RelayPlane solves that problem with cost-optimized routing: it sends simple requests to cheaper models and complex requests to more capable ones automatically, reducing costs by up to 40% without manual configuration changes.
Use both: they solve different layers of the same problem
RelayPlane and the Vercel AI SDK are complementary. The AI SDK handles the frontend streaming layer and provider abstraction beautifully. RelayPlane sits underneath as the proxy that governs cost, enforces policies, and routes intelligently. Using both gives you a complete stack: great streaming UI on top, cost intelligence and governance underneath.
Use both: RelayPlane + Vercel AI SDK
The most common setup is to use both tools together. The Vercel AI SDK handles the frontend streaming experience: typed provider calls, partial token rendering, and clean React hooks. RelayPlane runs underneath as the proxy layer: tracking what each call costs, routing to the cheapest capable model, and alerting when spend thresholds are crossed.
To wire them together, set the baseURL in your provider configuration to http://localhost:4100/v1. The Vercel AI SDK sends its requests to RelayPlane, which logs the cost and forwards the request to the real provider. Your streaming UI works exactly as before. You just gain full cost visibility and governance on every call.
npm install -g @relayplane/proxy && relayplane start
// Point your Vercel AI SDK provider at the proxy
const openai = createOpenAI({ baseURL: 'http://localhost:4100/v1' })
When the Vercel AI SDK is the right fit
If you are building a Next.js application with a chat interface, the Vercel AI SDK is excellent. It abstracts away the differences between providers, handles streaming correctly across SSR and client boundaries, and ships with React hooks that make partial token rendering straightforward. It also supports structured object generation and tool calls out of the box.
For teams building user-facing AI products in React and Next.js, the Vercel AI SDK reduces boilerplate significantly. It is free, well-maintained, and widely adopted. RelayPlane does not replace it and does not try to.
When RelayPlane is the right fit
If you are running agents, AI coding tools, or any LLM-heavy workload and you need to understand what it costs, RelayPlane is the right tool. It installs in 30 seconds, proxies every LLM call through localhost, and stores cost and latency data locally with no cloud dependency.
RelayPlane also handles the routing layer: if a task is simple, it routes to a cheaper model automatically. If an agent is in a runaway loop, it stops the calls before the bill arrives. These are production-traffic concerns that a streaming library does not address.