Rust Didn't Win Because It's Fast
GitHub rewrote Copilot's runtime in Rust. OpenAI's Codex is now almost all Rust. Bun, the runtime Claude Code ships on, moved 535,496 lines of Zig to Rust in 11 days. But it isn't about speed: C has been fast for half a century. We fly inside a real laptop, down to the CPU die and the memory cells, to show what Rust actually changed, and why AI coding agents love it.
0:00 Everyone is rewriting in Rust
0:49 This is Sidequest Explained
1:00 Inside the machine: instructions, bytes, stack and heap
1:53 Way one: freeing memory by hand (C and C++)
2:23 An elevator crash started Rust
2:40 Way two: the garbage collector (Discord's spikes)
3:12 Way three: ownership
3:36 Checked before it runs, and Android's results
4:07 Close to the metal: 28 bytes vs 8
4:21 Copilot: 5.25 s to 292 ms
4:41 Why AI agents love the Rust compiler
5:11 Is Python dead? What it means for you
Sources
GitHub Blog, migrating the Copilot runtime to Rust (Sep 2026): github.blog
Bun, Rewriting Bun in Rust (Jul 2026): bun.sh
OpenAI Codex repository: openai/codex
Codex native rewrite discussion: codex#1174
Grok Build repository: xai-org/grok-build
Dennis Ritchie, The Development of the C Language: bell-labs.com
Microsoft MSRC, 70% of security bugs are memory safety (2019): microsoft.com
Chromium memory safety: chromium.org
MIT Technology Review, Rust's origin (2023): technologyreview.com
Rust 1.0 announcement: blog.rust-lang.org
Discord, Why Discord is switching from Go to Rust (2020): discord.com
The Rust Book, ownership and borrowing: doc.rust-lang.org
Google, memory-safe languages in Android 13 (2022): security.googleblog.com
Google, Rust in Android (Nov 2025): blog.google
Python sys.getsizeof / CPython ints: docs.python.org
Hugging Face tokenizers: huggingface/tokenizers
OpenAI tiktoken: openai/tiktoken
pydantic-core: pydantic/pydantic-core
uv by Astral: astral-sh/uv
Numbers are the sources' own. The Copilot timings are client + session + one-turn overhead in the opt-in in-process mode, not counting the model or network. Android's 1000× is memory-safety vulnerability density. Code on screen is an illustration, not a run.
Credits
Die micrographs: Fritzchens Fritz (CC0). Memory-cell micrograph (Micron MT4C1024) and SEM plate (1886VE10): ZeptoBars, CC BY 3.0. Office and hardware photos: Pexels. HDRIs and materials: Poly Haven, ambientCG (CC0). Music: "Lofi Study" by FASSounds (Pixabay). Rust, GitHub, Copilot, OpenAI, Codex, Bun, Claude, xAI, Grok, Microsoft, Chrome, Android, Discord, Python, Hugging Face, Astral, pydantic and other names and logos belong to their owners, used for identification and commentary; Sidequest is not affiliated with any of them. Narration: an AI clone of my own voice. Animation: original, built in three.js.
#rust #programming #ai
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Mentions
Rust Didn't Win Because It's Fast GitHub rewrote Copilot's runtime in Rust. OpenAI's Codex is now almost all Rust. Bun, the runtime Claude Code ships on, moved 535,496 lines of Zig to Rust in 11 days. But it isn't about speed: C has been fast for half a century. We fly inside a real laptop, down to the CPU die and the memory cells, to show what Rust actually changed, and why AI coding agents love it. 0:00 Everyone is rewriting in Rust 0:49 This is Sidequest Explained 1:00 Inside the machine: instructions, bytes, stack and heap 1:53 Way one: freeing memory by hand (C and C++) 2:23 An elevator crash started Rust 2:40 Way two: the garbage collector (Discord's spikes) 3:12 Way three: ownership 3:36 Checked before it runs, and Android's results 4:07 Close to the metal: 28 bytes vs 8 4:21 Copilot: 5.25 s to 292 ms 4:41 Why AI agents love the Rust compiler 5:11 Is Python dead? What it means for you Sources GitHub Blog, migrating the Copilot runtime to Rust (Sep 2026): github.blog Bun, Rewriting Bun in Rust (Jul 2026): bun.sh OpenAI Codex repository: openai/codex Codex native rewrite discussion: codex#1174 Grok Build repository: xai-org/grok-build Dennis Ritchie, The Development of the C Language: bell-labs.com Microsoft MSRC, 70% of security bugs are memory safety (2019): microsoft.com Chromium memory safety: chromium.org MIT Technology Review, Rust's origin (2023): technologyreview.com Rust 1.0 announcement: blog.rust-lang.org Discord, Why Discord is switching from Go to Rust (2020): discord.com The Rust Book, ownership and borrowing: doc.rust-lang.org Google, memory-safe languages in Android 13 (2022): security.googleblog.com Google, Rust in Android (Nov 2025): blog.google Python sys.getsizeof / CPython ints: docs.python.org Hugging Face tokenizers: huggingface/tokenizers OpenAI tiktoken: openai/tiktoken pydantic-core: pydantic/pydantic-core uv by Astral: astral-sh/uv Numbers are the sources' own. The Copilot timings are client + session + one-turn overhead in the opt-in in-process mode, not counting the model or network. Android's 1000× is memory-safety vulnerability density. Code on screen is an illustration, not a run. Credits Die micrographs: Fritzchens Fritz (CC0). Memory-cell micrograph (Micron MT4C1024) and SEM plate (1886VE10): ZeptoBars, CC BY 3.0. Office and hardware photos: Pexels. HDRIs and materials: Poly Haven, ambientCG (CC0). Music: "Lofi Study" by FASSounds (Pixabay). Rust, GitHub, Copilot, OpenAI, Codex, Bun, Claude, xAI, Grok, Microsoft, Chrome, Android, Discord, Python, Hugging Face, Astral, pydantic and other names and logos belong to their owners, used for identification and commentary; Sidequest is not affiliated with any of them. Narration: an AI clone of my own voice. Animation: original, built in three.js. #rust #programming #ai