Nemotron 3 Ultra 550B

Overview

nemotron-3-ultra-550b is NVIDIA’s flagship open-weight model and the strongest US open-weight on the Artificial Analysis index (AA Index 48). It is a 550B mixture-of-experts model (55B active parameters) with a hybrid Mamba-Transformer architecture, a 1M context window, and throughput above 300 tokens/second. Reach for it when you want top open-weight reasoning and coding with fast generation.

Specs

Field	Value
Model ID	`nemotron-3-ultra-550b`
Best for	Reasoning, coding, general work, long context, fast throughput
Context window	1M
Max output tokens	32K
Input modalities	Text
Output modalities	Text
Tool calling	Yes
Structured outputs	Yes
Reasoning	Yes
Prompt caching	Yes
Speed	Fast
Cost band	Balanced
Release stage	Stable

Use this when

You want the strongest US open-weight model for reasoning and coding.
You need high throughput on long generations.
You need a very large (1M) context window.
You build agents that need reliable tool calling and JSON outputs.

Pick something else when

You want the strongest tool-heavy agent: use kimi-k2.6.
You want the highest general quality: use qwen-3.7-plus.
You want deep step-by-step reasoning at lower cost: use deepseek-r1.

Example

from openai import OpenAI

client = OpenAI(base_url="https://kymaapi.com/v1", api_key="ky-...")

response = client.chat.completions.create(
    model="nemotron-3-ultra-550b",
    messages=[{"role": "user", "content": "Derive the time complexity and propose a faster algorithm."}]
)

Agent query example

curl "https://kymaapi.com/v1/models?recommended_for=reasoning&tools=true&quality_tier=frontier-open"

GPT-OSS 120B Step 3.7 Flash

​Overview

​Specs

​Use this when

​Pick something else when

​Example

​Agent query example