---
license: cc-by-4.0
tags:
  - pixel-canary
  - callstack-apex
  - stealth-model
  - stealthmark
  - coding
  - reasoning
thumbnail: https://stealthmodels.com/pixel-canary/assets/social-card-v3.png
---

<img src="https://huggingface.co/stealth-model/pixel-canary/resolve/main/panels/hero.webp" alt="Golden Pixel Canary building a small app beside the words 'Revealed as Callstack Apex'.">

**Our reasoning study pointed to Qwen two days before Callstack revealed Pixel Canary as Apex, a Qwen-based coding model built for React Native.**

By [Stealth Models](https://stealthmodels.com/).

<img src="https://huggingface.co/stealth-model/pixel-canary/resolve/main/panels/verdict.webp" alt="StealthMark 1.8.10 results for Pixel Canary (Callstack Apex): benchmark score 49.5, General Intelligence 40.4, Visual Intelligence 59.6. Strongest at characters that interact: 76.8 on Raccoon.">

<img src="https://huggingface.co/stealth-model/pixel-canary/resolve/main/panels/results.webp" alt="Every StealthMark result of Pixel Canary (Callstack Apex): Raccoon 76.8, Selfie 74.1, Beach 61.4, Mona Lisa 45.9, Ground Truth 44.1, Newton's Mirror 32.7, Latch 100.0 (partial run, 1 of 5 levels). Not tested yet: Foresight.">

[Compare it with the Qwen 3.8 family](https://stealthmodels.com/benchmarks?models=qwen3.8-max-0902,qwen3.8-27b,pixel-canary,qwen3.8-flash,qwen3.6-27b)

<img src="https://huggingface.co/stealth-model/pixel-canary/resolve/main/panels/case.webp" alt="The case file. First seen 25 Sep 2026, revealed 1 Oct 2026, developer Callstack (Poland), context 262,144 tokens, input Text, tool calls unknown, speed in our tests about 255 tok/s. 26 Sep 2026: A tokenizer study by AI時短ラボ links its vocabulary to Qwen. 29 Sep 2026, our finding: Our reasoning study puts Qwen3.8-Flash closest, two days before the reveal. 1 Oct 2026: Callstack reveals Apex: a Qwen foundation with React Native post-training.">

[See our reasoning study](https://stealthmodels.com/pixel-canary#reasoning-comparison)

<details><summary>Facts as text</summary>

| Fact | Value |
|---|---|
| First seen | 25 Sep 2026 |
| Revealed | 1 Oct 2026 |
| Developer | Callstack (Poland) |
| Context | 262,144 tokens |
| Input | Text |
| Tool calls | unknown |
| Speed in our tests | about 255 tok/s |
| Access | Active as a hosted API |

</details>

## Run it
Callstack serves Apex as a hosted model, so there are no weights to download.

---
[StealthMark leaderboard](https://huggingface.co/spaces/stealth-model/stealthmark)<br>
Text and images: CC BY 4.0, stealthmodels.com.