Evaluation results
A 9B model that decisively moves the base. Across the six reported metrics, Tess-4-9B improves on Qwen3.5-9B-Base every time:
- MMLU: 79.4%, up 56.2 points over the base and 21.9 points over Qwythos-9B.
- GSM8K: 88.0% in both flexible and strict scoring; strict accuracy is up 37 points over the base.
- GPQA Diamond: 62% at a 24K generation cap, reaching 73% with extended context.
- ARC-Challenge: 58.0% accuracy and 53.0% normalized accuracy.
The comparison includes Qwen3.5-9B-Base, Qwythos-9B, and Tess-4-9B. Scores are accuracy on a 0–1 scale in the chart. For GPQA, the solid Tess segment is the complete 24K-cap run (62%); only samples that exhausted that cap were retried at 48K, producing the lighter extension to 73%.
Why Tess-4 is different
- 🧠 Weight-scaled reasoning. Tess-4 keeps routine steps tight and pours deliberation into the hard ones — planning, debugging, synthesis, and judgment calls. It does not ramble; it thinks proportionally to the difficulty of the moment.
- 🛠️ Agentic by design. Native, parallel tool use and disciplined multi-step problem solving. It reads a codebase, builds a real mental model, and acts on it.
- 📏 Long-context, trained at 64K. Post-trained on 64K-token long-context agentic traces, so it can hold a large working set without losing the thread.
- 👁️ Multimodal. Inherits Qwen3.5's vision tower — text and image in.
- 🤝 Honest, not sycophantic. Trained to give grounded, evidence-based pushback instead of flattery.
- ⚡ A practical 9B footprint. Full BF16 weights are about 19 GB, making the model substantially easier to deploy and iterate with than its 27B sibling.
The reasoning traces
Tess-4's signature is how it thinks. The reasoning/thinking traces used to train it were a best-case approximation of Fable-5, produced by Opus-4.8, GPT-5.5, and GLM-5.2 working together as a team — a multi-model teacher ensemble distilled into a single, coherent reasoning style.
The result is a model that reasons prospectively — predicting, verifying, and weighing alternatives before acting — rather than narrating after the fact.
Tess-4 uses the bundled Qwen3.5-family agentic chat template with explicit <think> … </think> reasoning blocks. The model reasons first, then produces its visible answer:
<|im_start|>userYour prompt here<|im_end|><|im_start|>assistant<think>… the model's private reasoning …</think> … the model's answer …<|im_end|>
Apply the format automatically with tokenizer.apply_chat_template(messages, add_generation_prompt=True). Keep the repository's bundled chat template intact; substituting a generic template can materially change behavior.
Tess-4-9B is a heavy reasoner on difficult questions. For demanding math, science, or agentic tasks, allow a generous generation budget. Some GPQA samples required more than 24K output tokens and benefited from a 48K cap.
This repository — full-precision weights:
Table with columns: Format, Parameters, Approximate size, Best for| Format | Parameters | Approximate size | Best for |
|---|
| BF16 safetensors | 9.65B | 19.3 GB | transformers · vLLM · SGLang |
GGUF builds → migtissera/Tess-4-9B-GGUF
Table with columns: File, Format, Size, Best for| File | Format | Size | Best for |
|---|
| Tess-4-9B-Q4_K_M.gguf | Q4_K_M | 5.63 GB | recommended for most local users |
| Tess-4-9B-Q6_K.gguf | Q6_K | 7.36 GB | excellent quality/size balance |
| Tess-4-9B-Q8_0.gguf | Q8_0 | 9.53 GB | effectively lossless for most use cases |
| Tess-4-9B-F16.gguf | F16 | 17.92 GB | unquantized GGUF · maximum fidelity |
Quickstart
llama.cpp / LM Studio (GGUF)
Run the recommended Q4_K_M build directly from Hugging Face with a recent llama.cpp:
llama-cli \ -hf migtissera/Tess-4-9B-GGUF:Q4_K_M \ --jinja \ -c 65536 \ -p "Inspect this code, identify the root cause, and propose a verified fix."
Or download it first:
hf download migtissera/Tess-4-9B-GGUF \ Tess-4-9B-Q4_K_M.gguf \ --local-dir ./tess-4-9b
See the Tess-4-9B-GGUF model card for every quant, llama.cpp server commands, memory guidance, and prompt-format details. The current GGUF release contains text-model files only; use this full-precision repository for the inherited vision path.
Use a recent transformers release with Qwen3.5 support.
from transformers import AutoProcessor, AutoModelForImageTextToTextimport torch model_id = "migtissera/Tess-4-9B" processor = AutoProcessor.from_pretrained( model_id, trust_remote_code=True,)model = AutoModelForImageTextToText.from_pretrained( model_id, torch_dtype=torch.bfloat16, device_map="auto", trust_remote_code=True,) messages = [ { "role": "user", "content": "Inspect this function, identify the bug, and propose a verified fix.", }] inputs = processor.apply_chat_template( messages, tokenize=True, add_generation_prompt=True, return_dict=True, return_tensors="pt",).to(model.device) outputs = model.generate( **inputs, max_new_tokens=8192, do_sample=False,) prompt_tokens = inputs["input_ids"].shape[-1]answer = processor.decode( outputs[0][prompt_tokens:], skip_special_tokens=True,)print(answer)
For multimodal input, pass image and text content through AutoProcessor using the standard Qwen3.5 message structure.
What it is good at
- Agentic coding — exploring unfamiliar repositories, planning changes, and executing multi-step work with tools.
- Long-context work — reasoning over large codebases and documents without dropping context.
- Hard reasoning — allocating substantial inference-time thought to math, science, debugging, and synthesis.
- Technical and product judgment — honest, structured analysis that pushes back with evidence rather than agreeing by default.
- Local and single-GPU experimentation — a strong reasoning profile in a much more deployable parameter class.
Credits
Tess-4-9B is built on Qwen/Qwen3.5-9B-Base by the Qwen team — full credit to them for an outstanding base model. Tess-4 inherits its Qwen3.5 vision-language architecture and its Apache 2.0 license.
License
Released under the Apache License 2.0, inherited from the base model.
Citation
@misc{tissera2026tess49b, title = {Tess-4-9B}, author = {Migel Tissera}, year = {2026}, howpublished = {\url{https://huggingface.co/migtissera/Tess-4-9B}}, note = {Built on Qwen/Qwen3.5-9B-Base}}
Tess-4-9B — part of the Tess series by Migel Tissera.