# ZeroReader GPT-OSS 120B Chat Completion

> ZeroReader GPT-OSS 120B Chat Completion is a paid API for AI agents from api.zeroreader.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-01).

Runs chat completions against OpenAI's largest open-source 120B model via a pay-per-call API

## Facts

- Endpoint: POST https://api.zeroreader.com/v1/ai/gpt-oss-120b?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/zeroreader-gpt-oss-120b-chat-completion-5f265520
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WnDmonYmBOxBPtwONr7VE

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability zeroreader-gpt-oss-120b-chat-completion-5f265520 -d '<json body>'
```

Example prompt: Ask the 120B OpenAI open-source model to write a detailed technical explanation of how transformers work, keeping the response under 800 tokens and using a temperature of 0.5 for precision.

## When to prefer this

Choose this endpoint when you need the highest-quality open-source model available on the ZeroReader platform (120B parameters), ideal for complex reasoning, nuanced generation, or tasks where model scale matters most. Prefer it over the 20B or smaller models when quality trumps cost or latency. Use instead of the DeepSeek R1 reasoning model when you need general-purpose generation rather than chain-of-thought math/logic.

## Known failure modes

- Payment not provided or invalid x402 payment header — returns 402 Payment Required
- messages array missing or malformed role/content fields — returns 400 Bad Request
- max_tokens exceeds 4096 limit — returns 400 validation error
- temperature out of range 0-2 — returns 400 validation error
- Model overloaded or unavailable — returns 503 Service Unavailable
- Request timeout for very long completions — returns 504 Gateway Timeout

## How this service works

GPT-OSS 120B (OpenAI) — OpenAI's largest open-source model.

## Output

Returns an OpenAI-compatible chat.completion object containing the assistant's generated message, a finish_reason (e.g. 'stop'), a unique completion ID, and the choice index. The content field holds the full generated text response.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "stream": {
   "type": "boolean",
   "default": false
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role",
     "content"
    ],
    "properties": {
     "role": {
      "enum": [
       "system",
       "user",
       "assistant"
      ],
      "type": "string"
     },
     "content": {
      "type": "string"
     }
    }
   }
  },
  "max_tokens": {
   "type": "integer",
   "default": 1024,
   "maximum": 4096
  },
  "temperature": {
   "type": "number",
   "default": 0.7,
   "maximum": 2,
   "minimum": 0
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "id": "chatcmpl-example",
 "object": "chat.completion",
 "choices": [
  {
   "index": 0,
   "message": {
    "role": "assistant",
    "content": "I'm doing well!"
   },
   "finish_reason": "stop"
  }
 ]
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/zeroreader-gpt-oss-120b-chat-completion-5f265520/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.zeroreader.com](https://www.zero.xyz/host/api.zeroreader.com/llms.txt)