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---
title: "Zen4 Ultra: 480B Parameters, 1M Token Context"
description: "Zen4 Ultra is our most capable model: 480B total parameters, 35B active per token, 1M token context window. Benchmark results and use cases."
date: "2026-01-20"
author: "Zen LM Team"
tags: ["Models", "Zen4", "Flagship"]
---
[GITHUB](https://github.com/hanzoai) [HUGGING FACE](https://huggingface.co/hanzoai/zen4-ultra) [TRY ZEN CHAT](https://hanzo.ai/chat)
**Zen4 Ultra** is the most capable model in the Zen4 family. It is a Mixture of Diverse Experts (MoE) model with 480B total parameters and 35B active parameters per forward pass. The native context window is 256K tokens, extending to 1M tokens with YaRN extrapolation.
## Architecture
Property| Value
---|---
Total parameters| 480B
Active parameters per token| 35B
Experts per layer| 128
Top-k routing| 8
Context window (native)| 256K
Context window (YaRN)| 1M
Vocabulary size| 151,936
Attention heads| 64
KV heads (GQA)| 8
Layers| 94
## Benchmark Results
### General Reasoning
Benchmark| Zen4 Ultra| Zen Max 72B
---|---|---
MMLU| 89.4| 87.1
MMLU-Pro| 75.2| 71.8
ARC-Challenge| 72.1| 68.4
HellaSwag| 92.3| 90.1
Winogrande| 87.6| 85.2
### Mathematics
Benchmark| Zen4 Ultra| Zen Max 72B
---|---|---
MATH| 81.4| 73.2
GSM8K| 95.3| 92.1
AMC 2023| 62.4| 54.7
AIME 2024| 48.2| 37.6
### Code
Benchmark| Zen4 Ultra| Zen Max 72B
---|---|---
HumanEval| 91.2| 82.4
MBPP| 87.6| 81.3
LiveCodeBench| 52.4| 44.1
SWE-bench Verified| 45.7| 38.2
### Long Context
Task| Score at 32K| Score at 128K| Score at 512K
---|---|---|---
NIAH recall| 99.1%| 98.4%| 94.7%
Summarization| 48.2| 46.9| 43.1
QA over long doc| 74.3| 71.2| 64.8
Long-context performance remains strong through 512K tokens, with graceful degradation thereafter.
### Multilingual
Evaluated on 30 languages across MMMLU:
Language Group| Score
---|---
Latin script (high-resource)| 86.4
Latin script (low-resource)| 72.1
CJK| 81.3
Arabic/Hebrew| 76.8
Other non-Latin| 68.2
## Use Cases
### Complex Research and Analysis
Zen4 Ultra excels at tasks requiring synthesis across long documents:
* Analyzing regulatory filings spanning hundreds of pages
* Cross-referencing scientific literature for systematic reviews
* Multi-document legal analysis with citation tracking
* Financial model analysis with full spreadsheet context
The 1M token context allows loading entire codebases, large document sets, or extended conversation histories without truncation.
### Multi-Step Reasoning
For problems requiring planning and backtracking — competitive math, logic puzzles, complex software architecture decisions — Ultra’s depth provides measurable advantage over smaller models.
### Agentic Workflows
Ultra’s function calling reliability is critical for long-running agent tasks:
* SWE-bench Verified: 45.7% (full-repo software engineering tasks)
* Tool selection accuracy: 94.2% on held-out tool-use evaluation
* Multi-turn instruction adherence: 91.8%
### Code Generation
Near-human performance on competitive programming tasks. Generates complete, working implementations of complex algorithms in all major languages.
## Running Zen4 Ultra
### Hugging Face + vLLM (recommended for production)
```python
from vllm import LLM, SamplingParams
llm = LLM(
model="hanzoai/zen4-ultra",
tensor_parallel_size=8, # 8x H100 80GB
max_model_len=131072,
)
outputs = llm.generate(
["Explain the Zen MoDE architecture in detail."],
SamplingParams(temperature=0.7, max_tokens=2048),
)
```
### Transformers
```python
from transformers import AutoModelForCausalLM, AutoTokenizer
import torch
model = AutoModelForCausalLM.from_pretrained(
"hanzoai/zen4-ultra",
torch_dtype=torch.bfloat16,
device_map="auto",
)
tokenizer = AutoTokenizer.from_pretrained("hanzoai/zen4-ultra")
messages = [{"role": "user", "content": "Solve: find all integer solutions to x^3 + y^3 = z^3."}]
text = tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
inputs = tokenizer(text, return_tensors="pt").to(model.device)
output = model.generate(**inputs, max_new_tokens=1024)
print(tokenizer.decode(output[0][inputs.input_ids.shape[1]:], skip_special_tokens=True))
```
### Hardware Requirements
Configuration| VRAM| Throughput
---|---|---
8x H100 80GB| 640GB| ~2,400 tok/s
16x A100 80GB| 1280GB| ~1,100 tok/s
32x A100 40GB| 1280GB| ~600 tok/s
For cost-sensitive production use cases, [Zen Max 72B](/blog/zen-max/) delivers most of Ultra’s capability at a fraction of the compute.
## License
Apache-2.0. Commercial use permitted. No royalty or usage fees.
* * *
_Zen4 Ultra is available now on[Hugging Face](https://huggingface.co/hanzoai/zen4-ultra). For API access, see [hanzo.ai](https://hanzo.ai)._