Compatible APIs

Point existing OpenAI-compatible (and selected native) clients at NexLLM. Change two values — base URL and API key — and keep the provider request format you already use. Spend lands on your www.nexllm.ai wallet.

Introduction

NexLLM is an OpenAI-compatible AI gateway. The commercial path for apps, scripts, and IDE plugins is:

https://www.nexllm.ai/v1

Authentication for standard OpenAI-shaped requests:

Authorization: Bearer YOUR_NEXLLM_API_KEY

Endpoint	Format	When to use
`POST /v1/chat/completions`	OpenAI Chat Completions	Default for chat / tools / streaming
`POST /v1/responses`	OpenAI Responses	When you need the Responses API shape
`POST /v1/completions`	Legacy text completions	Older prompt-only clients
`POST /v1/embeddings`	OpenAI embeddings	RAG / search
`POST /v1/images/generations`	OpenAI images	Text-to-image
`POST /v1/images/edits`	OpenAI image edits	Edit / inpaint style flows
`POST /v1/audio/transcriptions`	OpenAI STT	Speech-to-text
`POST /v1/audio/speech`	OpenAI TTS	Text-to-speech
`POST /v1/rerank`	Rerank	Document ranking
`GET /v1/models`	Models list	Discover IDs for your key
`POST /v1/messages`	Anthropic Messages	Native Claude request shape
`GET /v1/realtime`	Realtime (WebSocket)	Realtime sessions when enabled for your key

Full field reference: API Reference. Agent-side tools instead of app code: MCP integration.

Model IDs are whatever GET /v1/models returns for your API key (channel group + key restrictions). Examples in this page (gpt-4o, aws/claude-haiku-4-5) are illustrative — always confirm live IDs for your account.

Prerequisites

A NexLLM account and API key (Getting your API keys)
Wallet balance for paid calls (Wallet)
Any client that accepts a configurable OpenAI base_url / baseURL, or Anthropic base_url for Messages

OpenAI Chat Completions

Quick start (cURL)

curl https://www.nexllm.ai/v1/chat/completions \
  -H "Authorization: Bearer $NEXLLM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4o",
    "messages": [
      {"role": "user", "content": "Write a one-line product tagline."}
    ],
    "max_tokens": 100
  }'

OpenAI Python SDK

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_NEXLLM_API_KEY",
    base_url="https://www.nexllm.ai/v1",
)

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Write a one-line product tagline."}],
    max_tokens=100,
)

print(response.choices[0].message.content)

OpenAI TypeScript / Node SDK

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.NEXLLM_API_KEY,
  baseURL: "https://www.nexllm.ai/v1",
});

const response = await client.chat.completions.create({
  model: "gpt-4o",
  messages: [{ role: "user", content: "Write a one-line product tagline." }],
  max_tokens: 100,
});

console.log(response.choices[0]?.message?.content);

Streaming

Set "stream": true (or stream: true in the SDK). The SSE shape matches OpenAI Chat Completions (choices[0].delta.content, ending with data: [DONE]).

stream = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Tell me a short joke."}],
    stream=True,
)

for chunk in stream:
    delta = chunk.choices[0].delta.content or ""
    print(delta, end="", flush=True)

OpenAI Responses

Use when your stack targets /v1/responses instead of Chat Completions. Confirm the model’s supported_endpoint_types via GET /v1/models first.

response = client.responses.create(
    model="gpt-4o",
    input="Write a one-line product tagline.",
)
print(response.output_text)

See API Reference and Migrate from Vercel AI Gateway for Responses notes with the Vercel AI SDK.

Anthropic Messages (native)

NexLLM also accepts Anthropic’s Messages shape at POST /v1/messages. Pass your NexLLM key in x-api-key (and include anthropic-version), or use Bearer auth as documented in Authentication.

curl https://www.nexllm.ai/v1/messages \
  -H "x-api-key: $NEXLLM_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "aws/claude-haiku-4-5",
    "max_tokens": 100,
    "messages": [{"role": "user", "content": "Write a short welcome message."}]
  }'

Images

curl https://www.nexllm.ai/v1/images/generations \
  -H "Authorization: Bearer $NEXLLM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "dall-e-3",
    "prompt": "A product hero shot on a clean studio background",
    "n": 1,
    "size": "1024x1024"
  }'

Confirm an image-capable model ID with GET /v1/models. Details: Image Generation API. For Vercel AI SDK apps, chat uses @ai-sdk/openai against this same base URL; images can use the OpenAI SDK/HTTP path or @nexllm/ai-sdk-provider — see Vercel AI SDK.

Discover models for your key

curl https://www.nexllm.ai/v1/models \
  -H "Authorization: Bearer $NEXLLM_API_KEY"

Use the exact data[].id values in later calls. Channel groups and key restrictions change the catalog — see Channel groups and Models API.

Key differences vs calling OpenAI directly

Aspect	OpenAI	NexLLM
Base URL	`https://api.openai.com/v1`	`https://www.nexllm.ai/v1`
API key	OpenAI key	NexLLM key (`Authorization: Bearer …`)
Model IDs	OpenAI catalog	Your channel-group catalog (GPT, Claude, Gemini, and more)
Billing	OpenAI account	NexLLM wallet
Request / response shape	OpenAI schema	Same OpenAI schema on compatible endpoints

When to use Compatible APIs vs MCP vs Skills

Need	Use
App / backend / SDK code	Compatible APIs (this page)
Claude / Cursor / other agents with tools	MCP integration
Outcome recipes on top of MCP	Skills
Next.js / Vercel AI SDK chat	Vercel AI SDK

Billing

Compatible API calls use standard gateway rates for the model and endpoint. There is no separate “compatible API” surcharge. See Pricing overview and Wallet.

Troubleshooting

401 / authentication failed

Confirm Authorization: Bearer uses a NexLLM key (not an OpenAI or Vercel gateway key). Check expiry, IP allowlist, and whitespace. See Authentication.

Model not found

Call GET /v1/models with the same key. Use the exact id. Check the key’s channel group and any model allowlist on the key.

Insufficient balance

Top up the wallet and retry. Usage logs are under Usage.

Wrong endpoint for this model

Some models only support Chat Completions, Responses, or Messages. Inspect supported_endpoint_types on GET /v1/models before switching shapes.

Quickstart
API Reference
Authentication
MCP integration
Skills
Vercel AI SDK
Migrate from OpenRouter and other migrations

​Introduction

​Prerequisites

​OpenAI Chat Completions

​Quick start (cURL)

​OpenAI Python SDK

​OpenAI TypeScript / Node SDK

​Streaming

​OpenAI Responses

​Anthropic Messages (native)

​Images

​Discover models for your key

​Key differences vs calling OpenAI directly

​When to use Compatible APIs vs MCP vs Skills

​Billing

​Troubleshooting

​Related

Introduction

Prerequisites

OpenAI Chat Completions

Quick start (cURL)

OpenAI Python SDK

OpenAI TypeScript / Node SDK

Streaming

OpenAI Responses

Anthropic Messages (native)

Images

Discover models for your key

Key differences vs calling OpenAI directly

When to use Compatible APIs vs MCP vs Skills

Billing

Troubleshooting

Related