---
license: mit
library_name: transformers
tags:
- preserved
- repository-exploration
- subagent
- coder
- agentic
- qwen3
- 256k
- long-context
language:
- en
pipeline_tag: text-generation
---

![banner](banner.png)

<div style="border:2px solid currentColor; font-family:ui-monospace,'SF Mono','Cascadia Mono',Consolas,'Liberation Mono',monospace;">
  <div style="border-bottom:1px solid currentColor; padding:6px 12px; font-size:11px; letter-spacing:3px; text-transform:uppercase; opacity:0.7; text-align:center;">PRESERVED ORIGINAL // REMOVED BY MICROSOFT FROM HF + GITHUB // MIT</div>
  <div style="padding:14px; display:flex; flex-wrap:wrap; align-items:center; justify-content:center; gap:18px;">
<pre style="margin:0; flex:0 0 auto; font-family:ui-monospace,'SF Mono','Cascadia Mono',Consolas,monospace; font-size:9px; line-height:1.15; letter-spacing:0;">
   microsoft/FastContext ──▶ 404
   github.com/microsoft/FastContext ──▶ 404
              │
              ▼
   ┌──────────────────────────┐
   │  weights preserved here  │
   │  bf16 · 8.0 GB · intact  │
   └──────────────────────────┘
     you can't un-open-source
</pre>
    <div style="flex:0 1 auto; max-width:100%; text-align:center;">
      <div style="font-size:23px; font-weight:800; letter-spacing:1px;">FASTCONTEXT-1.0-4B-SFT</div>
      <div style="font-size:12.5px; letter-spacing:1px; opacity:0.8; margin-top:5px;"><span style="white-space:nowrap;">PRESERVED ORIGINAL WEIGHTS</span> · <span style="white-space:nowrap;">QWEN3 DENSE 4B</span> · <span style="white-space:nowrap;">256K CONTEXT</span> · <span style="white-space:nowrap;">BF16 · 8.0 GB</span></div>
    </div>
  </div>
  <table style="display:table; table-layout:fixed; width:100%; margin:0; border-collapse:collapse; font-family:ui-monospace,'SF Mono',Consolas,monospace; font-size:12px;">
    <tr>
      <td style="border-top:1px solid currentColor; border-right:1px solid currentColor; padding:8px 12px;"><div style="font-size:10px; letter-spacing:1px; opacity:0.6;">WEIGHTS</div><div style="font-weight:700;">BF16 · UNMODIFIED</div></td>
      <td style="border-top:1px solid currentColor; border-right:1px solid currentColor; padding:8px 12px;"><div style="font-size:10px; letter-spacing:1px; opacity:0.6;">ARCH</div><div style="font-weight:700;">QWEN3 DENSE · 36L</div></td>
      <td style="border-top:1px solid currentColor; border-right:1px solid currentColor; padding:8px 12px;"><div style="font-size:10px; letter-spacing:1px; opacity:0.6;">CONTEXT</div><div style="font-weight:700;">256K NATIVE</div></td>
      <td style="border-top:1px solid currentColor; padding:8px 12px;"><div style="font-size:10px; letter-spacing:1px; opacity:0.6;">LICENSE</div><div style="font-weight:700;">MIT</div></td>
    </tr>
  </table>
</div>

> Microsoft open-sourced FastContext under MIT, then **deleted it from both HuggingFace and GitHub** about two weeks later (verified: 404 on both, 2026-07-02). MIT means preservation is legal — so here it is, unmodified. **Own your AI: a model on your disk can't be sunset by a quarterly review.**

## 🔍 What it is

A **repository-exploration subagent** for coding agents. Invoked on demand by your main agent, it fires **parallel read-only tool calls** (`READ` / `GLOB` / `GREP`) across a repo and returns **only the file paths + line ranges that matter**, as compact context. Your frontier coding agent stops wasting its context window (and your bill) crawling the file tree.

Microsoft's (now-deleted) announcement reported **~60% fewer tokens** from the main coding agent and **+5.5% on SWE-bench** — their figures; the source no longer exists to cite.

**Architecture**: plain `Qwen3ForCausalLM` dense 4B — 36 layers, 256K native context. No exotic modules; loads with standard `transformers`.

## 🚀 Quick start

```python
from transformers import AutoModelForCausalLM, AutoTokenizer
m = AutoModelForCausalLM.from_pretrained("KikoCis/FastContext-1.0-4B-SFT", torch_dtype="bfloat16", device_map="auto")
tok = AutoTokenizer.from_pretrained("KikoCis/FastContext-1.0-4B-SFT")
```

**Don't want 8 GB?** Grab the **GGUF quants** (1.96–2.5 GB, long-context imatrix, retrieval-validated 30/30 vs this bf16):
👉 [KikoCis/FastContext-1.0-4B-longctx-imatrix-GGUF](https://huggingface.co/KikoCis/FastContext-1.0-4B-longctx-imatrix-GGUF)

## ⚠️ Good to know

- It's a **scout, not a solver** — it finds and returns evidence; pair it with a main coding agent that writes the actual fix.
- Upstream docs, harness code and issues were deleted along with the repos; usage conventions here come from the announcement and community mirrors.
- Weights are **byte-identical** to the (re-uploaded) original — no fine-tuning, no edits.

## 📚 Credit & license

Model, weights, training: **© Microsoft** (MIT). This is a preservation mirror sourced via the `ShaunGves/FastContext-1.0-4B-SFT` re-upload after `microsoft/FastContext-1.0-4B-SFT` was removed. Nothing modified. Quantized companion + validation: KikoCis.