Hermes 4 405B API

Hermes 4 is a large-scale reasoning model built on Meta-Llama-3.1-405B with hybrid reasoning mode. It can choose to deliberate internally with ... traces or respond directly, offering flexibility between speed and depth. Supports structured outputs, JSON mode, function calling, and tool use.

Modalities: TextText
In / Out price: $1.06/$3.17per 1M
Context window: 128K tokens
Released: Oct 2, 2025

Hermes 4 405B overview

Hermes 4 405B by NousResearch

Its hybrid reasoning mode allows users to switch between fast, direct responses and deep, step-by-step analysis.

Hermes 4 405B specs

Model ID: nousresearch/hermes-4-405b
Developer: NousResearch
Context window: 131,072 tokens
Max output: 16,000 tokens
Input: Text
Output: Text
API: OpenAI-compatible, base URL https://api.aimlapi.com/v1

Hermes 4 405B API

Hermes 4 405B is a state-of-the-art, hybrid reasoning language model developed by Nous Research, built on the foundation of Meta’s Llama-3.1-405B. It is designed for advanced reasoning, structured outputs, and flexible user control, making it a top choice for demanding AI applications in math, code, STEM, and logical reasoning tasks.

Technical Specifications

Base Architecture: Built on Llama-3.1-405B, one of the largest open-weight transformer models.
Parameter Count: 405 billion parameters.
Training Data: Instruction-tuned with ~60 billion tokens of high-quality post-training data, with heavy emphasis on reasoning traces.

Performance Benchmarks

Math & Logic: Outperforms previous Hermes models and rivals leading closed-source models in math, code, and logical reasoning tasks.
STEM & Creativity: Excels in scientific, technical, and creative writing, with improved format-faithful outputs.
General Assistant: Maintains broad utility for general-purpose tasks, with high coherence in multi-turn conversations.
Speed vs. Depth: Hybrid reasoning mode allows users to choose between fast direct responses and deeper deliberation with explicit reasoning traces.

Key Features

Hybrid Reasoning Mode: Users can toggle between fast, direct responses and detailed, trace-based reasoning using the reasoning boolean flag.‍
Steerability: Highly customizable, with improved alignment and lower refusal rates for user-directed tasks.‍
Large Context: Handles long documents and complex multi-step tasks.

Comparison with Other Models

vs Llama-3.1 Instruct: Hermes 4 405B offers superior reasoning, structured outputs, and steerability, with a larger post-training corpus and hybrid reasoning mode.

vs GPT-4.1 nano: Hermes 4 405B matches or exceeds GPT-4.1 nano in intelligence and reasoning, with a much larger context window and lower refusal rates.

vs Hermes 3: Hermes 4 features a 50x larger training dataset, improved reasoning traces, and enhanced schema adherence and function calling.

vs Claude 3: Hermes 4 405B excels in math, code, and structured outputs, with a focus on user control and neutrality.

Use cases

Advanced Reasoning: Ideal for math, logic, and STEM problem-solving.
Code Generation: Reliable for code synthesis, debugging, and technical documentation.
Creative Writing: Supports creative storytelling, roleplaying, and subjective responses.
Enterprise Integration: Suitable for enterprise assistants, chatbots, and workflow automation.

Capabilities

Function calling
Streaming
Structured outputs

Hermes 4 405B API pricing

Hermes 4 405B pricing in US dollars
Usage	Price	Unit
Input	$1.06	1M tokens
Output	$3.17	1M tokens
Cached input	$1.06	1M tokens

Prices from the AI/ML API price list, checked on Nov 4, 2026.

Hermes 4 405B vs other models: token prices

AI/ML API input and output rates for 5 models, per million tokens.

AI/ML API model prices in USD per million tokens
Model	Input	Output
Hermes 4 405B	$1.06	$3.17
Hermes 3 70B Instruct	$0.7406	$0.7406
Hermes 3 405B Instruct	$1.06	$1.06
Seed 2.0 Code	$0.529	$3.17
Glimpse	$0.6348	$3.17

How to use the Hermes 4 405B API

View docs

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key

export AIMLAPI_KEY="8f2b4c7d9a1e6b3f…"

2Make your first request

curl 'https://api.aimlapi.com/v1/chat/completions' \
  -H "Authorization: Bearer $AIMLAPI_KEY" \
  -H 'Content-Type: application/json' \
  -d '{
  "model": "nousresearch/hermes-4-405b",
  "messages": [
    {
      "role": "user",
      "content": "Write a haiku about the ocean."
    }
  ]
}'

import os
import requests

headers = {
    "Authorization": f"Bearer {os.environ['AIMLAPI_KEY']}",
    "Content-Type": "application/json",
}
payload = {
    "model": "nousresearch/hermes-4-405b",
    "messages": [
        {
            "role": "user",
            "content": "Write a haiku about the ocean."
        }
    ]
}

response = requests.post("https://api.aimlapi.com/v1/chat/completions", headers=headers, json=payload, timeout=120)
response.raise_for_status()
print(response.json())

const response = await fetch("https://api.aimlapi.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "model": "nousresearch/hermes-4-405b",
    "messages": [
      {
        "role": "user",
        "content": "Write a haiku about the ocean."
      }
    ]
  }),
});

if (!response.ok) throw new Error(`HTTP ${response.status}`);
console.log(await response.json());

All posts

Hermes 4 405B FAQ

What is the context window of Hermes 4 405B?

Hermes 4 405B has a 131,072 tokens context window and can return up to 16,000 tokens.

What inputs and outputs does Hermes 4 405B support?

Hermes 4 405B takes text as input and returns text.

What is the model ID for Hermes 4 405B?

Use nousresearch/hermes-4-405b as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.

When was Hermes 4 405B released?

Hermes 4 405B became available on October 2, 2025.

How much does Hermes 4 405B cost?

Hermes 4 405B costs $1.06 input and $3.17 output per 1M tokens on AI/ML API, billed as you go with no subscription.

Does Hermes 4 405B support streaming?

Yes, Hermes 4 405B can stream responses as they are generated.

Who created Hermes 4 405B?

Hermes 4 405B was built by NousResearch.

Does Hermes 4 405B support a hybrid reasoning or thinking mode?

Yes. It can choose to use internal <think> traces for deliberation or respond directly, balancing speed and depth.

Which API endpoint provides access to Hermes 4 405B?

It is available via the endpoint https://api.aimlapi.com/v1/chat/completions.

Does Hermes 4 405B support function calling and tool use?

Yes, it supports function calling, parallel tool calls, and structured outputs.

Start building with Hermes 4 405B

Get API key

Hermes 4 405B API

nousresearch/hermes-4-405b

Build with your agent

Give your agent the model details, code and documentation.

1Get your API key

Create API key

export AIMLAPI_KEY="8f2b4c7d9a1e6b3f…"

2Make your first request

curl 'https://api.aimlapi.com/v1/chat/completions' \
  -H "Authorization: Bearer $AIMLAPI_KEY" \
  -H 'Content-Type: application/json' \
  -d '{
  "model": "nousresearch/hermes-4-405b",
  "messages": [
    {
      "role": "user",
      "content": "Write a haiku about the ocean."
    }
  ]
}'

import os
import requests

headers = {
    "Authorization": f"Bearer {os.environ['AIMLAPI_KEY']}",
    "Content-Type": "application/json",
}
payload = {
    "model": "nousresearch/hermes-4-405b",
    "messages": [
        {
            "role": "user",
            "content": "Write a haiku about the ocean."
        }
    ]
}

response = requests.post("https://api.aimlapi.com/v1/chat/completions", headers=headers, json=payload, timeout=120)
response.raise_for_status()
print(response.json())

const response = await fetch("https://api.aimlapi.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "model": "nousresearch/hermes-4-405b",
    "messages": [
      {
        "role": "user",
        "content": "Write a haiku about the ocean."
      }
    ]
  }),
});

if (!response.ok) throw new Error(`HTTP ${response.status}`);
console.log(await response.json());

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Hermes 4 405B API

Hermes 4 405B overview

Hermes 4 405B by NousResearch

Hermes 4 405B specs

Hermes 4 405B API

Technical Specifications

Performance Benchmarks

Key Features

Comparison with Other Models

Use cases

Capabilities

Hermes 4 405B API pricing

Hermes 4 405B vs other models: token prices

How to use the Hermes 4 405B API

Build with your agent

1Get your API key

2Make your first request

Related articles

Hermes 4 405B FAQ

Start building with Hermes 4 405B

Hermes 4 405B API

Build with your agent

1Get your API key

2Make your first request

Hermes 4 405B API

Hermes 4 405B overview

Hermes 4 405B by NousResearch

Hermes 4 405B specs

Hermes 4 405B API

Technical Specifications

Performance Benchmarks

Key Features

Comparison with Other Models

Use cases

Capabilities

Hermes 4 405B API pricing

Hermes 4 405B vs other models: token prices

How to use the Hermes 4 405B API

Build with your agent

1Get your API key

2Make your first request

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