Nemotron 3 Ultra 550B (Free)
nvidia/nemotron-3-ultra-550b
NVIDIA Nemotron 3 Ultra 550B-A55B, free. 550B total / 55B active MoE with a 1M-token context — the largest free model in the catalog.
Code Examples
from blockrun_llm import LLMClient
client = LLMClient() # Uses BLOCKRUN_WALLET_KEY (never sent to server)
response = client.chat("nvidia/nemotron-3-ultra-550b", "Hello!")Pricing
Free model — no payment or wallet required.
Payment
Pay per request with USDC on Base. No subscription required.
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About NVIDIA Nemotron 3 Ultra 550B (Free)
NVIDIA Nemotron 3 Ultra 550B-A55B, free. 550B total / 55B active MoE with a 1M-token context — the largest free model in the catalog. It is built by NVIDIA 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
Nemotron 3 Ultra 550B (Free) is free to call on BlockRun. No payment header is required, no wallet needs funding, and no API key is issued — requests are rate limited per IP rather than billed. It is a practical way to develop against the API surface before moving production traffic onto a paid model.
Specifications
- Context window
- 1,000,000 tokens
- Maximum output
- 16,384 tokens
- API compatibility
- OpenAI-compatible
- Payment
- Free — no payment required
- Categories
- chat, reasoning
Calling it from your code
Pass nvidia/nemotron-3-ultra-550b 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 76 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 Nemotron 3 Ultra 550B (Free):