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.
reasoning boolean flag.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.
Measured on the AI/ML API gateway across live traffic. Figures are medians unless stated. Last updated 2026-10-12.
import requests r = requests.post( "https://api.aimlapi.com/v1/chat/completions", headers={"Authorization": "Bearer " + AIMLAPI_KEY}, json={ "model": "nousresearch/hermes-4-405b", "messages": [ { "role": "user", "content": "Hello!" } ] }, ) print(r.json())
const r = 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": "Hello!" } ] }), }); console.log(await r.json());
curl -X POST 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":"Hello!"}]}'
OpenAI-compatible — swap the base URL and it works with your existing SDK.
| Type | Price |
|---|---|
| Input | |
| Output | |
| Cached input |
| Model | Input | Output | Context | Best for |
|---|---|---|---|---|
Hermes 4 405B This page | Coding + agents | |||
| Reasoning + agents | ||||
| Balanced coding + agents | ||||
| Long-context, multimodal & agentic workflows | ||||
| Reasoning + agents |
Hermes 4 405B has a 131,072 tokens context window and can return up to 16,000 tokens.
Hermes 4 405B takes text as input and returns text.
Use nousresearch/hermes-4-405b as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.
Hermes 4 405B became available on October 2, 2025.
Hermes 4 405B is priced at input $1.3754 / 1M tokens, output $4.1262 / 1M tokens, cached input $1.3754 / 1M tokens.
Yes, Hermes 4 405B can stream responses as they are generated.
Hermes 4 405B was built by NousResearch.
Yes. It can choose to use internal <think> traces for deliberation or respond directly, balancing speed and depth.
It is available via the endpoint https://api.aimlapi.com/v1/chat/completions.
Yes, it supports function calling, parallel tool calls, and structured outputs.
