API Gateway Comparison: Claude vs OpenAI vs Gemini

If you're searching for an API gateway comparison across Claude, OpenAI, and Gemini, you're probably trying to solve one of two problems: you want a single interface to call multiple model providers, or you want to turn one provider's access (often a Claude subscription) into a proper HTTPS API with keys, streaming, and usage tracking. These are related but different problems, and the right tool depends on which one you actually have.

This article breaks down the main categories of gateways — self-hosted proxies, multi-provider routers, and managed single-provider services — and where each one fits.

The three types of "API gateway" for LLMs

1. Self-hosted reverse proxies

Tools like Kong, Envoy, or a custom Express/FastAPI service sit in front of the Claude, OpenAI, and Gemini APIs. You write the routing logic yourself: which provider gets which request, how keys are stored, how rate limits are enforced.

Pros: full control, no vendor lock-in, you can route per-request based on cost or latency.

Cons: you own the infrastructure, the key rotation, the streaming edge cases (SSE reconnects, partial tool-call chunks), and the on-call pager when it breaks at 2am. For a small team, this is usually more engineering work than the problem justifies.

2. Multi-provider LLM routers

Open-source and commercial routers (LiteLLM, Portkey, OpenRouter) normalize the request/response shape across Claude, OpenAI, and Gemini so your application code doesn't need provider-specific branches. This is genuinely useful if your product needs to switch models dynamically — say, Gemini for cheap classification and Claude for long-context reasoning.

Pros: one SDK call shape regardless of backend model, built-in fallback if a provider has an outage.

Cons: normalization is lossy. Claude's tool-use format, Gemini's function-calling schema, and OpenAI's function format don't map 1:1. Edge cases around streaming tool calls, stop reasons, and token usage fields often get flattened or dropped. You're also trusting the router with every provider's credentials.

3. Managed single-provider API services

If your actual need is "I have Claude access and I want to expose it as a clean, production-grade API for my own app or team," a multi-provider router is overkill. This is the category SubToAPI sits in: it takes your existing Claude access and gives you sub_live_... application keys, streaming, tool use, and usage metadata per key — without you running infrastructure or normalizing three different APIs.

The tradeoff is scope: SubToAPI doesn't route to OpenAI or Gemini. It's purpose-built for teams whose stack is Claude-first and who want API-key management, team seats, and billing visibility without building it themselves.

What actually differs between Claude, OpenAI, and Gemini at the API level

Before picking a gateway, it's worth knowing what you're gatewaying. The three APIs are not interchangeable at the wire level:

• Message format. Claude uses a messages array with a separate system parameter. OpenAI folds system prompts into the messages array as a role. Gemini uses contents with parts.
• Streaming events. Claude streams typed SSE events (content_block_delta, message_stop, etc.). OpenAI streams data: chunks with delta objects. Gemini's streaming shape differs again. A gateway that normalizes streaming has to translate event semantics, not just JSON keys.
• Tool use. All three support function/tool calling, but the schema for defining tools and the shape of the model's tool-call response differ enough that a thin pass-through proxy won't make them compatible — you still need provider-aware client code somewhere.
• Usage metadata. Token counting and cost fields are reported differently, which matters if you're billing internal teams or customers per request.

A gateway comparison that ignores these differences will give you a false sense of portability. Switching providers under a normalized router still usually means testing prompts and tool schemas again.

How to choose

Ask three questions:

1. Do I need multiple providers, or one provider exposed properly? If you're committed to Claude for your product, a single-provider API layer is simpler and has fewer moving parts than a multi-provider router.
2. Who's calling the API — my own backend, or other developers/teams? If you need per-team or per-app keys, rate limits, and usage visibility, you want a service built for that, not a raw proxy you maintain yourself.
3. Do I need streaming and tool use to work exactly like the underlying provider, or is a normalized abstraction good enough? If your app depends on Claude's specific tool-use behavior, a pass-through API that doesn't reshape responses is safer than a normalizer.

If the answer leans toward "Claude, with proper key management for my app or team," a managed layer like SubToAPI is the fastest path: sign up, get application keys scoped to your Claude access, and start calling a stable HTTPS endpoint.

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

This gives you streaming (/docs/streaming), tool use (/docs/tools), and per-key usage tracking without building or hosting a gateway yourself. See /docs/quickstart and /docs/messages for the full request/response shape, and /pricing for plan details (Solo €9, Team €19/seat, Scale €49/seat, free trial at /signup).

If instead you genuinely need to route across Claude, OpenAI, and Gemini in the same product — say, for cost arbitrage or redundancy — a multi-provider router is the right category, but budget real engineering time for testing tool-use and streaming behavior per provider, since no gateway makes that difference disappear.

questions

Is there a single API gateway that makes Claude, OpenAI, and Gemini fully interchangeable? No. Multi-provider routers normalize request/response shapes, but tool-call schemas, streaming event formats, and usage metadata differ enough that you'll still need to test and often adjust prompts and tool definitions per provider.

Do I need a multi-provider gateway if my app only uses Claude? Usually not. A single-provider API layer purpose-built for Claude, like SubToAPI, gives you application keys, streaming, and usage data with less overhead than running a generic router you don't need.

What's the main risk of a self-hosted proxy for multiple LLM providers? You own key rotation, SSE streaming edge cases, rate limiting, and incident response. For most teams this is more ongoing engineering work than the abstraction saves.