GPT-5 API: One OpenAI-Compatible Key for the Whole GPT-5 Family

The GPT-5 API is how you put the GPT-5 family of models into your own software — chat apps, agents, coding assistants, batch pipelines, anything that can make an HTTPS request. ApiTopMix provides GPT-5 API access through a single OpenAI-compatible endpoint, so instead of wiring up a separate integration for each model, you get one GPT-5 API key that reaches the entire lineup: gpt-5, gpt-5.1, gpt-5.2, gpt-5.4, gpt-5.5 and gpt-5-mini. Point your base URL at https://apitopmix.com/v1, set the model field, and you are calling GPT-5.

Because the endpoint speaks the OpenAI protocol, this is the least disruptive way to add GPT-5 to an existing project. If you already have code built on the OpenAI SDK, it keeps working after you change only the GPT-5 API base URL and the key — no rewrite of your request logic, your streaming handlers, or your tool-calling code. Usage is pay-per-use and priced below the official rate, and everything — keys, spend, model access — lives in one ApiTopMix console. This guide walks through the model lineup, how to call it in Python and curl, how to migrate from the official OpenAI API, and how GPT-5 compares to Claude.

The GPT-5 model lineup on ApiTopMix

ApiTopMix exposes the full GPT-5 series through the same endpoint and the same key — you select a model purely by its id in the model field. The table below is your map from model id to what it is best for, with notes on how each fits into a real workload. It deliberately carries no prices: token rates change, so the authoritative, always-current numbers live on the pricing page. Use the "see live pricing" link before you commit any model to high volume.

See live pricing: the per-model, per-token rates for every id above are published on the ApiTopMix pricing page. All GPT-5 models are billed pay-per-use and sit below the official price, so a sensible strategy is to prototype on gpt-5 or gpt-5-mini, then move individual routes up to gpt-5.2, gpt-5.4 or gpt-5.5 only where the quality gain earns its cost.

How to call the GPT-5 API

Calling GPT-5 through ApiTopMix is the standard OpenAI Chat Completions flow with one change: the GPT-5 API base URL is https://apitopmix.com/v1. Below are the two forms you will use most — the official OpenAI Python SDK and a raw curl request. Both use your ApiTopMix sk- key and model="gpt-5"; swap in any other id from the lineup to switch models.

OpenAI Python SDK

from openai import OpenAI

client = OpenAI(
    base_url="https://apitopmix.com/v1",   # GPT-5 API base url
    api_key="sk-your-apitopmix-key",
)

resp = client.chat.completions.create(
    model="gpt-5",                          # or gpt-5.2, gpt-5.5, gpt-5-mini ...
    messages=[
        {"role": "system", "content": "You are a helpful assistant."},
        {"role": "user", "content": "Explain the GPT-5 API in one sentence."},
    ],
)
print(resp.choices[0].message.content)

curl

curl https://apitopmix.com/v1/chat/completions \
  -H "Authorization: Bearer sk-your-apitopmix-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5",
    "messages": [
      {"role": "user", "content": "Say hi from the GPT-5 API"}
    ]
  }'

Streaming, function/tool calling, temperature, max_tokens and the rest of the OpenAI Chat Completions parameters behave exactly as they do against the official API, because the endpoint mirrors that protocol. If your client asks for an "OpenAI Base URL", give it https://apitopmix.com/v1 — the same value works in the Node SDK (baseURL), LangChain (base_url), LlamaIndex (api_base), Cursor, Cline, ChatBox and more. For a per-client reference on exactly where that field lives, see the base URL cheat sheet.

Migrating from the official OpenAI API

If you are already calling OpenAI directly, moving to the GPT-5 API on ApiTopMix is a two-line change, not a migration project. The request and response shapes are identical, so your surrounding code — prompt construction, streaming, retries, tool schemas — stays exactly as it is. You change only:

1. The base URL — set base_url (Python) or baseURL (Node) to https://apitopmix.com/v1 instead of the default OpenAI endpoint.
2. The API key — replace your OpenAI key with your ApiTopMix sk- key.

That is the whole migration. Here is a typical before/after in Python:

# Before — official OpenAI
client = OpenAI(
    api_key="sk-openai-...",
)

# After — GPT-5 API via ApiTopMix
client = OpenAI(
    base_url="https://apitopmix.com/v1",   # add this line
    api_key="sk-your-apitopmix-key",       # swap the key
)

# everything below is unchanged
resp = client.chat.completions.create(
    model="gpt-5",
    messages=[{"role": "user", "content": "ping"}],
)

If you prefer to configure via environment variables, set the base URL your framework reads (for OpenAI-SDK-based tools this is typically OPENAI_BASE_URL) to https://apitopmix.com/v1, and point OPENAI_API_KEY at your ApiTopMix key. One practical benefit worth calling out: because ApiTopMix is a unified gateway with its own account, you can use the GPT-5 API without an OpenAI account — you only manage an ApiTopMix key and one bill, and the same key also reaches other model families on the platform by changing the model field.

GPT-5 vs Claude through ApiTopMix

A frequent question is whether to build on GPT-5 or on Claude. The pragmatic answer with ApiTopMix is that you do not have to choose up front: both families are reachable through the same OpenAI-compatible endpoint and the same key, so you can route different tasks to different models and compare them on your own prompts. In broad strokes, the GPT-5 family — especially gpt-5.2 through gpt-5.5 — is a strong all-round choice for reasoning, agents and coding, while Claude models are widely favored for long-context work, careful instruction following and coding assistants. Rather than argue it in the abstract, test both on your workload and let cost and quality decide.

If Claude is part of your plan, ApiTopMix serves it the same way, below official price. See the cheap Claude API guide for the Claude side of the lineup, and the Use Claude Code guide if you want to drive a coding agent through the same account.

Frequently asked questions

What is the GPT-5 API and how do I access it through ApiTopMix?

The GPT-5 API is the programmatic interface to the GPT-5 family. ApiTopMix provides GPT-5 API access through one OpenAI-compatible endpoint at https://apitopmix.com/v1. Create a single ApiTopMix key, point your client's base URL there, and set model to gpt-5, gpt-5.1, gpt-5.2, gpt-5.4, gpt-5.5 or gpt-5-mini. Because the endpoint speaks the OpenAI protocol, existing OpenAI SDK code works after you change only the base URL and key.

How do I get a GPT-5 API key?

Register at apitopmix.com, open the console, and create a key that starts with sk-. That single GPT-5 API key calls every model in the lineup, so there is no separate key per model. Paste it into your OpenAI-compatible client next to the base URL https://apitopmix.com/v1 and you can send requests immediately.

Is the GPT-5 API OpenAI compatible?

Yes — the endpoint implements the OpenAI Chat Completions protocol at https://apitopmix.com/v1. Any tool that lets you override the OpenAI base URL — the official Python and Node SDKs, LangChain, LlamaIndex, Cursor, Cline, ChatBox and others — can call GPT-5 by setting base_url to that value and choosing a GPT-5 model id. This is what makes it a GPT-5 API OpenAI compatible drop-in.

How do I migrate my existing OpenAI code to the GPT-5 API?

Change two things: set base_url/baseURL to https://apitopmix.com/v1, and swap your key for the ApiTopMix key. Leave messages, streaming, tools and temperature untouched, since the request and response shapes match the OpenAI protocol. Then set model to a GPT-5 id such as gpt-5 or gpt-5-mini. That two-line change is the entire GPT-5 API tutorial for existing OpenAI projects.

How much does the GPT-5 API cost?

ApiTopMix bills GPT-5 usage pay-per-use, priced below the official rate for the corresponding model. Cost is per token and varies by model, with gpt-5-mini costing less than the larger models. Because rates change, the live GPT-5 API pricing for each id is published on the pricing page rather than hard-coded here — check it before committing high volume. This is also the honest way to evaluate a cheap GPT-5 API: compare the live per-token rate against the official one.

Can I use the GPT-5 API without an OpenAI account?

Yes. ApiTopMix is a unified gateway with its own account and billing, so you can use the GPT-5 API without an OpenAI account — only an ApiTopMix key is required. You manage usage, keys and spend from the ApiTopMix console, and the same key reaches other model families by changing the model field.

What is the difference between gpt-5 and gpt-5-mini?

gpt-5 is the flagship for the hardest reasoning, coding and long-context tasks; gpt-5-mini is the smaller, faster, cheaper variant for high-volume, latency-sensitive and cost-sensitive work like classification, extraction and chat. They share the same interface, so you switch by changing only the model field. Many teams route bulk traffic to the GPT-5 mini API and escalate only hard requests to gpt-5 or a higher point release.

Which GPT-5 model should I use — gpt-5, gpt-5.2 or gpt-5.5?

Use gpt-5 as the dependable default and step up to gpt-5.1, gpt-5.2, gpt-5.4 or gpt-5.5 for the newer releases' gains on reasoning, instruction following and coding. Since every model shares one endpoint and key, prototype on gpt-5 or gpt-5-mini, A/B test the higher point releases on your own prompts, and keep whichever gives the best quality-to-cost ratio. Check live per-model rates on the pricing page first.

Related guides

• ApiTopMix Pricing — live per-model, per-token rates for every GPT-5 model and the rest of the catalog.
• Cheap Claude API — the Claude side of the lineup through the same key, below official price.
• Use Claude Code — drive a coding agent through your ApiTopMix account.
• API Base URL cheat sheet — where to paste https://apitopmix.com/v1 in every popular client.
• ApiTopMix API Documentation — endpoints, headers and full code samples.

Conclusion

The GPT-5 API does not have to mean a new account, a new SDK, or a rewrite. Through ApiTopMix you get one key, the OpenAI-compatible base URL https://apitopmix.com/v1, and the entire GPT-5 lineup — gpt-5, gpt-5.1, gpt-5.2, gpt-5.4, gpt-5.5 and gpt-5-mini — selectable by a single model field. Existing OpenAI code works by changing the base URL and key; billing is pay-per-use below official price; and the same key extends to Claude and other families when you need them.

The fastest path is to grab a key, change two lines, and run your existing prompts against gpt-5. From there, test gpt-5-mini for volume and the higher point releases for quality, and check the pricing page to keep the quality-to-cost trade-off honest. That is the whole loop — buy a GPT-5 API key, point at the endpoint, and ship.