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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!")

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

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About OpenAI GPT-OSS 120B

Open-weight 120B model (Apache 2.0), flagship open model. Available on testnet for developer testing. It is built by OpenAI and served through BlockRun's OpenAI-compatible API, which means you can call it without an account, an API key, or a subscription. Requests are paid for individually, in USDC, at the moment they are made.

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 comes back as an HTTP 402 carrying a signed price quote. Your client signs that quote with a wallet holding USDC and retries; the second request returns the completion, and the payment settles on-chain. Client libraries handle this handshake for you, so in practice it is a single call. See the documentation for request and response shapes, or browse the full catalog of 71 chat models to compare alternatives.

Related models

Every model on BlockRun is reached through the same endpoint and the same payment flow, so switching is a one-line change to the model field. These are the closest alternatives to GPT-OSS 120B: