BlockRun
Get started
Back to Models

GPT-OSS 120B

openai/gpt-oss-120b

openai

Open-weight 120B model (Apache 2.0), flagship open model. Available on testnet for developer testing.

Code Examples

from blockrun_llm import LLMClient

# Testnet: Use testnet API endpoint
client = LLMClient(api_url="https://testnet.blockrun.ai/api")
response = client.chat("openai/gpt-oss-120b", "Hello!")
import { LLMClient } from '@blockrun/llm';

// Testnet: Use testnet API endpoint
const client = new LLMClient({ apiUrl: 'https://testnet.blockrun.ai/api' });
const response = await client.chat('openai/gpt-oss-120b', 'Hello!');
curl -X POST https://testnet.blockrun.ai/api/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <payment_header>" \
  -d '{
    "model": "openai/gpt-oss-120b",
    "messages": [{"role": "user", "content": "Hello!"}],
    "max_tokens": 1024
  }'

Pricing

Per Request$0.0030
Context128K tokens
Max Output16K tokens

Flat rate per request. No token counting.

Payment

Network
Base Sepolia
Currency
Testnet USDC
Protocol
x402

Pay per request with testnet USDC on Base Sepolia. Get testnet USDC from Circle faucet.

Try It

Send a message to try GPT-OSS 120B

Connect your wallet to enable payments

About OpenAI GPT-OSS 120B

GPT-OSS 120B is a reasoning and coding model from OpenAI with a 128K-token context window and up to 16K tokens of output per call. It is billed at a flat rate per request rather than per token. It is served on the Base Sepolia testnet and paid in testnet USDC. It is served through BlockRun's OpenAI-compatible API, so it can be called without an account, an API key, or a subscription.

What it costs

GPT-OSS 120B is billed at a flat $0.0030 per request, settlement fee included, regardless of how long the prompt or the completion runs. Flat pricing makes cost per call predictable for high-volume agent loops where token counts vary widely from request to request.

Specifications

Context window
128,000 tokens
Maximum output
16,384 tokens
API compatibility
OpenAI-compatible
Payment
USDC via x402
Categories
chat, reasoning, coding

Calling it from your code

Pass openai/gpt-oss-120b as the model field. Because the endpoint mirrors the OpenAI chat completions schema, any existing OpenAI client works by changing the base URL — streaming, tool use, and multi-turn messages all behave the same way.

The first request returns a 402 carrying the exact price; a signed retry runs it, and client libraries fold the two into one call — how the payment works. See the documentation for request and response shapes, the LLM API page for every model on this endpoint, or browse the full catalog of 78 chat models to compare alternatives.