Claude API Gateway for Multiple Apps: Setup Guide

If you're building more than one product on top of Claude — a mobile app, an internal tool, a customer-facing chatbot — you've probably hit the same wall: Anthropic's console gives you one account and one way of tracking usage, but you need separate credentials, separate rate limits, and separate billing visibility per application. A Claude API gateway solves this by sitting between your apps and Claude, issuing distinct keys per project while routing everything through a single underlying account.

This matters because mixing all your apps under one raw API key makes it impossible to answer basic questions: which app is burning through tokens, which one is hitting rate limits, which one needs a key rotated after a leak. A gateway gives you that separation without needing five different Anthropic accounts or five different billing relationships.

Why a Single Claude API Key Doesn't Scale Across Projects

When you have one API key shared across multiple apps, you run into a few recurring problems:

• No per-app usage breakdown. You see total token consumption, but not which app is responsible for it.
• Shared rate limits. A traffic spike in one app can throttle requests from an unrelated app.
• Security blast radius. If one app's key leaks (committed to a public repo, exposed in a mobile bundle), you have to rotate the key used by every app simultaneously.
• No per-team or per-client isolation. If you're an agency or a platform serving multiple clients, you can't easily segment usage or revoke access for just one of them.

A gateway architecture fixes this by introducing an application layer of API keys that map back to one Claude account. Each app gets its own key, its own usage ledger, and can be revoked independently.

What a Claude API Gateway Actually Does

At its core, a gateway for Claude does three things:

1. Issues scoped API keys — one per app, team, or client, instead of sharing a single raw key.
2. Proxies requests to Claude's Messages API — forwarding prompts, handling streaming, and returning responses in a predictable format.
3. Tracks usage per key — so you can see token counts, request volume, and cost attribution broken down by application.

This is exactly the problem SubToAPI is built around. Instead of managing one Claude credential across every project, you generate separate sub_live_... keys for each app from a single dashboard, each hitting the same underlying Claude access but reported and billed independently.

Setting This Up in Practice

Here's a typical pattern for a team running three products — a web app, a Slack bot, and an internal admin tool — all needing Claude access.

1. Create one SubToAPI account, multiple keys

Sign up once at /signup, then generate a distinct key per application from the dashboard. Name them clearly:

• web-app-prod
• slack-bot-prod
• internal-admin

2. Point each app at the same gateway endpoint

All apps call the same base URL, just with different keys:

curl https://api.subtoapi.app/v1/messages \
  -H "Authorization: Bearer $SUBTOAPI_KEY_WEBAPP" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Summarize this ticket for a support agent."}
    ]
  }'

const res = await fetch("https://api.subtoapi.app/v1/messages", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.SUBTOAPI_KEY_SLACKBOT}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    model: "claude-sonnet-4-5",
    max_tokens: 1024,
    messages: [{ role: "user", content: "Draft a reply to this Slack message." }],
  }),
});

Each key is independent: rotating the Slack bot's key doesn't touch the web app, and a traffic spike from the admin tool doesn't exhaust the web app's quota because usage is tracked and reported per key.

3. Use streaming and tools consistently across apps

Because every app talks to the same gateway API, you don't need to reimplement Claude integration logic three times. Streaming works the same way for every key — see /docs/streaming — and tool calling follows the same request format across apps, documented at /docs/tools. This means your Slack bot and your web app can share the same internal SDK wrapper, just swapping the API key via environment variable.

4. Review usage per app, not per account

Instead of one lump sum of token usage, you get a breakdown by key in the dashboard. This is useful for:

• Deciding which app justifies upgrading from Solo to Team.
• Spotting an app with runaway token usage (e.g., a prompt that got too long after a bad deploy).
• Billing internal teams or external clients based on actual consumption.

When to Add Team Seats Instead of More Keys

If multiple people need to manage or monitor the same app's Claude usage — not just multiple apps — that's a seat problem, not a key problem. SubToAPI's Team plan (€19/seat) and Scale plan (€49/seat) add multiple dashboard users with their own logins, while still letting you issue as many application keys as you need under the same account. Pricing details are at /pricing.

A common setup: one SubToAPI account on Team, three application keys (web, mobile, internal tool), and two team members who can both see usage dashboards and rotate keys without sharing a single login.

Getting Started

If you're currently sharing one Claude API key across multiple codebases, the migration path is straightforward: sign up, generate one key per app, swap the Authorization header in each codebase, and keep the rest of your integration unchanged — request format, streaming, and tool use all follow the standard Messages API shape. Start with /docs/quickstart if you're setting this up for the first time, or /docs/messages if you're migrating an existing integration.

FAQ

Can I use one Claude account for multiple unrelated apps? Yes. A gateway like SubToAPI lets you issue separate API keys per app while they all draw from the same underlying Claude access, so you don't need multiple Anthropic accounts or billing relationships.

Does each app need its own rate limit? Rate limits are tied to your plan, but separating apps into distinct keys means you can identify which app is consuming the most capacity and plan upgrades (Solo, Team, or Scale) accordingly rather than guessing from aggregate usage.

What happens if one app's API key is compromised? You revoke and regenerate that single key from the dashboard. Other apps using their own keys are unaffected, since each key is scoped and tracked independently.