Chat & messages

OneHop speaks the protocols your SDK already uses. Point the base URL at the right family, pass a OneHop model slug, and your existing client works unchanged.

Family	Base URL	Endpoints
OpenAI-compatible	`https://api.onehop.ai/v1`	`chat/completions`, `responses`
Anthropic-compatible	`https://api.onehop.ai/anthropic`	`v1/messages`
Google GenAI / Vertex	`https://api.onehop.ai/vertex-ai`	`models/{model}:generateContent`

The request and response bodies are passed through to the upstream provider. OneHop only reads model, stream, and a little usage metadata — it does not rewrite your payload, so tool calls, system prompts, and message shapes behave exactly as the provider documents them.

Chat completions (OpenAI)

curl https://api.onehop.ai/v1/chat/completions \
  -H "Authorization: Bearer $ONEHOP_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.5",
    "messages": [{ "role": "user", "content": "Explain prepaid billing in one line." }]
  }'

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.ONEHOP_API_KEY,
  baseURL: "https://api.onehop.ai/v1",
});

const completion = await client.chat.completions.create({
  model: "openai/gpt-5.5",
  messages: [{ role: "user", content: "Hello from OneHop" }],
});

Streaming

Set stream: true and read server-sent events as usual. OneHop streams chunks straight through without buffering the whole response, and bills the real usage once the upstream finishes.

curl https://api.onehop.ai/v1/chat/completions \
  -H "Authorization: Bearer $ONEHOP_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.5",
    "stream": true,
    "messages": [{ "role": "user", "content": "Stream a haiku" }]
  }'

Disconnects abort upstream

If your client disconnects mid-stream, OneHop aborts the upstream request. You are billed for usage the provider actually reported; otherwise the record is reconciled or marked failed.

Anthropic messages

The recommended Anthropic entry point is /anthropic/v1/messages. Use the x-api-key header, just like the native Anthropic SDK.

curl https://api.onehop.ai/anthropic/v1/messages \
  -H "x-api-key: $ONEHOP_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-opus-4.8",
    "max_tokens": 256,
    "messages": [{ "role": "user", "content": "Hello from OneHop" }]
  }'

Responses & Vertex

Responses: POST /v1/responses (or the short alias POST /responses) for clients built on the OpenAI Responses protocol.
Vertex / Gemini: point at https://api.onehop.ai/vertex-ai and call :generateContent / :streamGenerateContent with the model in the path.

To see which protocols a given model supports, filter the catalog — /v1/models?protocol=anthropic_messages. See Models & discovery for the full filter list.

Chat & messages

Chat completions (OpenAI)

Streaming

Anthropic messages

Responses & Vertex

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