Best LLM Gateway for Claude and OpenAI in 2025

If you're searching for "best LLM gateway for Claude and OpenAI," you're probably trying to solve one of two problems: you want a single API key and billing layer across both providers, or you've hit the limits of raw provider access (no per-app keys, no usage breakdown, no team seats) and need something that behaves like a real production API. The honest answer is that "best" depends on which problem you have — a universal multi-provider router and a hardened, provider-specific API layer solve different things, and conflating them causes most of the frustration teams run into.

This article breaks down what an LLM gateway actually does, the criteria that matter when evaluating one, and where a Claude-focused tool like SubToAPI fits versus a multi-provider abstraction layer.

What an LLM gateway actually does

Strip away the marketing and an LLM gateway is usually some combination of:

• Key management — issuing scoped API keys per app, environment, or customer instead of sharing one root credential.
• Request normalization — a consistent request/response shape regardless of which model answers.
• Usage metering — token counts, cost, and request logs per key, not just a provider-wide invoice.
• Streaming and tool use support — passing through SSE streams and function-calling/tool schemas without breaking them.
• Team access — seats, roles, and shared billing instead of everyone using one personal account.

Some tools try to do this across every provider at once (Claude, OpenAI, Gemini, open models). Others focus deeply on one provider and do that one thing well. Both are legitimate "gateways" — they just optimize for different tradeoffs.

The multi-provider gateway tradeoff

A universal gateway's pitch is simple: one API, swap models by changing a string, avoid vendor lock-in. In practice, this introduces its own costs:

• Lowest-common-denominator features. Claude's extended tool use, prompt caching, and response metadata don't map 1:1 onto OpenAI's function calling. Abstraction layers tend to flatten both down to whatever overlaps, which means you lose provider-specific capability instead of gaining it.
• Debugging gets harder. When a request fails, you now have two layers to check: your gateway's translation logic and the upstream provider's actual behavior.
• You rarely actually swap providers. Most teams pick Claude or GPT for a specific task (reasoning quality, latency, cost, tool-calling reliability) and stick with it. The "provider-agnostic" promise is often insurance you pay for every month and never use.

If your product genuinely routes traffic across multiple model providers based on cost or load — fine, a universal router earns its keep. If you're mostly running Claude in production and just need it to behave like a normal, billable, multi-key API, a provider-specific layer is usually faster to adopt and easier to reason about.

Where a Claude-specific API layer wins

This is the gap SubToAPI fills. It takes the Claude access you already have and turns it into a standard HTTPS API with:

• Per-application keys in the sub_live_... format, so each app, environment, or client gets its own credential instead of one shared account.
• Full streaming support for real-time responses.
• Tool use (function calling) passed through correctly.
• Usage metadata per key, so you can see what each app is actually costing.
• Team seats on a shared dashboard, so a whole team can work off one Claude plan without passing around a single login.

It's not trying to also be your OpenAI gateway — it's a focused layer on top of Claude, which means there's no translation logic between you and the model's actual capabilities.

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 changelog in 3 bullets."}
    ]
  }'

For streaming or tool-enabled requests, the request shape stays the same — see the messages docs, streaming docs, and tools docs for the specifics.

Decision framework

Ask these questions before picking a gateway:

1. Are you actually load-balancing across providers in production, or just future-proofing? If it's the latter, you're paying complexity tax for a scenario that may never happen.
2. Do you need provider-specific features (tool use, caching, long context) at full fidelity, or a generic chat completion? Abstraction layers cost you fidelity.
3. Is your real pain "multiple providers" or "no per-app keys / no usage breakdown / no team access"? Most teams discover it's the second one — which a provider-specific API layer solves directly, without the overhead of a routing layer.
4. Who's debugging this at 2am? Fewer layers between you and the model means fewer places for things to silently break.

A pragmatic setup

For most teams building on Claude, the fastest path is:

• Use a Claude-specific gateway (like SubToAPI) to get proper key management, streaming, tool use, and usage data without building that infrastructure yourself.
• If you also need OpenAI, call OpenAI's API directly with its own native key — you don't need to force both providers through one abstraction to get the benefits of each.
• Keep the two integrations separate in code if your product only ever uses one model per request type. It's simpler to maintain than a routing layer you built "just in case."

You can start with a free trial and get an application key issued in a couple of minutes — see the quickstart for the full setup, pricing for plan details, or just go to signup directly.

Pricing shape to expect

Provider-specific gateways tend to price per seat rather than per request, since the underlying model cost is already billed through your Claude access. SubToAPI's plans run Solo at €9, Team at €19/seat, and Scale at €49/seat, with a free trial at signup — no separate token markup layered on top.

Questions

Does a gateway replace my provider's API key entirely? For Claude, yes — a tool like SubToAPI issues its own application keys (sub_live_...) that sit in front of your account, so your apps never hold the raw provider credential directly.

Should I use one gateway for both Claude and OpenAI? Only if you're genuinely routing traffic between them in production. If you mainly use Claude, a Claude-specific layer gives you full feature fidelity and less debugging surface than a universal router.

What's the minimum feature set a Claude gateway should have? Per-app API keys, streaming, tool use support, and per-key usage metadata. Without those, you're not really running a production API — you're sharing one account.