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The Pulse: What can we learn from Bun’s rapid Rust rewrite with AI?

Bun creator Jarred Sumner used Anthropic's Fable AI to rewrite the JavaScript runtime from Zig to Rust in 11 days, costing $165,000 in tokens, a task that would have taken a small team a year. The migration highlights how AI can dramatically accelerate software rewrites, though it requires a thoroughly tested codebase. Meanwhile, coding LLM competition intensifies as Anthropic, OpenAI, Cursor, and Meta release new models, and North Korean hackers continue to target remote companies using AI-generated identities.

read2 min views1 publishedJul 9, 2026
The Pulse: What can we learn from Bun’s rapid Rust rewrite with AI?
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A rewrite done in 11 days that would have taken a small team a year to complete, for $165K in tokens. Also: coding LLM “wars” heat up, AI fakers from North Korea still a problem when hiring, and more

The Pulse is a series covering events, insights, and trends within Big Tech and startups. Notice an interesting event or trend? Hit reply and share it with me.

Today, we cover:

Bun’s Rust rewrite with Fable: what can we learn? To a sceptic, spending $165K to migrate Bun from Zig to Rust sounds very expensive. But to a realist, shortening a 1-2 year migration down to 11 days opens amazing new opportunities for devs. However, a thoroughly-tested project is required to pull it off.Anthropic’s Fable, OpenAI’s GPT-5.6 Sol, Cursor’s Grok 4.5, Meta’s Muse. Coding LLM wars heat up: Fable is back, OpenAI releases a comparable GPT-5.6 Sol, Cursor offers cheap & very capable Grok 4.5, and Meta is back with its first truly competitive coding model since Llama 3. But how did Gemini slip out of the top-ranked AI coding models?North Korean hackers keep trying to infiltrate full-remote companies. The founder of a Canadian digital consultancy caught a North Korean dev red-handed, using an AI filter. These events are now so common that it’s hard to trust remote interviewees are who they claim.Industry Pulse. Meta’s key logging exposed sensitive data, massive cuts at Xbox, Meta could not buy enough AI capacity from Google, Qualcomm acquires Modular, and memory price hikes hit Apple products.

1. Bun’s Rust rewrite with Fable: what can we learn? #

Last week in San Francisco, I met Jarred Sumner, creator of JavaScript runtime, Bun, and was keen to learn more about the rewrite of Bun from Zig to Rust. But at the time, Jarred didn’t want to say too much, as the tool used for the migration, Fable, was out of action due to the US government imposing export controls.

Fortunately, the situation is now resolved and Fable is available globally, and Jarred has published a detailed post about the project. Before we get into the migration, some context:

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