Hermes 4 405B
VerifiedOpen-weight LLM with 131k context for complex text tasks.
About Hermes 4 405B
The model follows a transformer-based design optimized for extended sequences. Nous Research released it as open weights to support broad community access and modification. This approach prioritizes flexibility for developers working with substantial text inputs.
Its primary strengths lie in managing lengthy documents and multi-turn conversations without truncation. The open-weight nature allows independent evaluation and adaptation across hardware setups. Text modality keeps the focus on pure language modeling performance.
Researchers commonly use it for experiments in summarization, reasoning, and retrieval-augmented generation. Fine-tuning workflows benefit from the large context when adapting to specialized domains. Production deployments often target on-premise environments where control over model weights is essential.
Capabilities
How Hermes 4 405B compares
Hermes 4 405B (striped bar) vs other language models on intelligence, speed and price.
Price
USD per 1M output tokens · Lower is better · Hermes 4 405B ranks #66 of 78
Sources: Artificial Analysis (intelligence, speed) · OpenRouter (price).
Best for
Long Document Analysis
Processes and reasons over extensive inputs up to 131072 tokens, making it suitable for summarizing research papers or legal contracts with sustained accuracy.
Agentic Tool Integration
Leverages tool use and function calling alongside multi-step planning to build reliable autonomous workflows for data retrieval or automation tasks.
Creative Narrative Development
Supports role-playing and creative writing with advanced instruction following, enabling consistent character development across multi-turn storytelling sessions.
Strengths & limitations
Strengths
- +Strong adherence to complex instructions
- +Effective handling of 128k context
- +Good at agentic and tool-augmented workflows
- +Open weights enabling customization
Limitations
- –Text-only modality
- –High inference compute requirements
- –May exhibit typical LLM hallucinations
Cost calculator
Estimate what Hermes 4 405B would cost for your usage.
Based on Hermes 4 405B's $1.00/1M input · $3.00/1M output. Estimate only — actual cost varies by provider and caching.
Download & self-host Hermes 4 405B
This is an open-weight model. Download the weights from Hugging Face or load it directly with Transformers.
# Install the Hugging Face CLI
pip install -U "huggingface_hub[cli]"
# Download the model weights
hf download NousResearch/Hermes-4-405B
# Or load it directly in Python
from transformers import AutoModelForCausalLM, AutoTokenizer
tok = AutoTokenizer.from_pretrained("NousResearch/Hermes-4-405B")
model = AutoModelForCausalLM.from_pretrained("NousResearch/Hermes-4-405B", device_map="auto")Quick start
OpenRouter's API is OpenAI-compatible — most SDKs work by just swapping the base URL. Only the model slug changes between models.
import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://openrouter.ai/api/v1",
apiKey: process.env.OPENROUTER_API_KEY,
});
const completion = await client.chat.completions.create({
model: "nousresearch/hermes-4-405b",
messages: [{ role: "user", content: "Hello!" }],
});
console.log(completion.choices[0].message.content);Model slug: nousresearch/hermes-4-405b
Editor's verdict
Hermes 4 405B is Nous Research's open-weight language models with a 131K-token context window.
At $3.00 per 1M output tokens, it is mid-priced for its class.
As an open-weight model you can self-host it (406B parameters) or call it through a hosted API.
Best suited to strong adherence to complex instructions and effective handling of 128k context.
Frequently asked questions
The model supports a context window of 131072 tokens.
User reviews
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