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Microsoft's agents ported Copilot's runtime to Rust for $120K

The Stack

Microsoft's agents ported Copilot's runtime to Rust for $120K

GitHub rewrote the engine behind Copilot from TypeScript to Rust, with AI agents doing most of the typing — and put a receipt on the whole project. GitHub says it ported the entire Copilot agent runtime to Rust, with agents writing the bulk of the code, for roughly $120,000 in tokens. The project — described by GitHub engineer Stephen Toub — started from a scoping estimate of about 130,000 lines of TypeScript and ended with more than 800,000 lines of production Rust, after roughly 430,000 lines

A 4B model mimics real students better than GPT-5.4

The Frontier

A 4B model mimics real students better than GPT-5.4

Two stories about where models are being pointed today: a student simulator that beats frontier models at being one particular learner, and Meituan's shopkeeper agent crossing a million restaurants. Microsoft researchers trained a 4B model to imitate individual students — and it beats GPT-5.4 and GPT-4o at the job. The system, called StudentSim, attacks a real bottleneck in AI tutoring: knowing which explanation works for which student requires watching real learners, and that feedback is slow,

Open Source Radar — September 20: where the agent actually runs

The Stack

Open Source Radar — September 20: where the agent actually runs

Today's board is unusually infrastructural. The fresh momentum is not another coding assistant but the layer underneath it: a model small enough to sit on the device, sandboxes that hand an agent a whole computer, a self-hosted control plane for the agents a company runs, and the parser that feeds documents to all of them. Needle 3 (Python, ~11,800 stars) — Cactus Compute's third generation of its tiny automation model: the whole thing is a single 8–29 MB binary at roughly 2 bits per weight, an

Google drafted state chatbot safety bills that exempt its own Gemini

The Guardrails

Google drafted state chatbot safety bills that exempt its own Gemini

State capitals spent 2026 passing laws about chatbots and children. An NPR investigation says one of the biggest chatbot makers helped write the language — and the language has holes in it. Google helped draft and lobby for chatbot-safety bills in at least ten states this year, and several of those bills contain carve-outs that could exempt the company's own Gemini from the rules, according to an NPR investigation by Katie McQue. The pattern is unusual for its simultaneity: identical or near-id

APUS reverse-engineers Jev into a fully offline browser agent

The Frontier

APUS reverse-engineers Jev into a fully offline browser agent

Jev's whole pitch was that decisions do not need generated text. Someone has now rebuilt that pitch with open weights, on a laptop, with the benchmark table to go with it. China's APUS AI Lab published fast-browser-use, an open-source reproduction of Jev's decision mechanics that runs entirely on local Qwen3.5 weights — no cloud endpoint, no API bill, MIT licensed. The project is not a wrapper around TypeSafe's hosted model, which is what Browser Use's own Jev Ultrafast was. APUS says it worked

Deep Dive — OpenAI's cash gap shrank while its compute bill grew

The Arena

Deep Dive — OpenAI's cash gap shrank while its compute bill grew

The leaked number everyone is quoting is the smaller one, and it got better. The Financial Times reported Friday that OpenAI expects negative free cash flow of $278 billion between 2026 and the end of 2030, according to a presentation the company prepared in July for a computing deal. The same materials put revenue at $350 billion in 2030 against roughly $36 billion this year, and compute and infrastructure at about $856 billion across the period. OpenAI declined to comment. The figures were co

Gartner lifts 2026 AI spending forecast to $2.7 trillion, up 49.5%

The Arena

Gartner lifts 2026 AI spending forecast to $2.7 trillion, up 49.5%

Two signals from the weekend, one about money and one about words: the AI spending forecast went up again, while the president of the United States ran a poll on what to call the technology. Gartner raised its forecast for worldwide AI spending in 2026 to $2.7 trillion, a 49.5% increase on 2025 — up from the $2.59 trillion and 47% growth the firm published in May. AI infrastructure, which the analyst house defines as AI-optimized cloud plus data-center construction, remains the largest single c

AI-exposed majors lose 5 points of hiring and 13% of starting pay

The Everyday

AI-exposed majors lose 5 points of hiring and 13% of starting pay

Two fresh data points land the same way: the money AI is saving is showing up as losses somewhere else — in the pay of the graduates who were supposed to build it, and in the electricity and hardware nobody budgeted for. Computer science graduates are entering the worst job market since the financial crisis, according to a new working paper from three US Census Bureau economists. Using administrative records on college graduates, the paper tracks how outcomes moved for majors with differing exp

AI 101 — AI vs machine learning: what's the difference?

The Frontier

AI 101 — AI vs machine learning: what's the difference?

Artificial intelligence is the goal — getting a machine to do things we would call intelligent — and machine learning is the technique the field now overwhelmingly uses to get there: instead of a programmer writing the rules, the system is handed examples and adjusts itself until its answers get better. The two terms get swapped for each other in almost every story you read, including ours. That is mostly harmless, and occasionally it hides the interesting part. When Justin Fanelli, the US Navy

SiliconFlow adds a C round on the way to its Hong Kong listing

The Arena

SiliconFlow adds a C round on the way to its Hong Kong listing

SiliconFlow closed new money on Sunday, and the interesting part is who signed: the same state system that buys its tokens is now taking equity in the meter. SiliconFlow has completed a second tranche of its B+ round and a C round, bringing its 2026 equity funding to nearly 2.9 billion yuan. The investor list reads like a state roll-call: China Internet Investment Fund, China Reform Fund, China Mobile's supply-chain fund, China Orient Asset International, Beijing Energy's fund, Shanghai Instrum

Google's leaked Mathematica shows the raw chain of thought

The Frontier

Google's leaked Mathematica shows the raw chain of thought

Two model stories where the interesting part is what the lab is willing to show: Google's internal math model runs on traces nobody has cleaned up, and StepFun finally put a date on open weights. An experimental Google model codenamed Mathematica has surfaced in leaked evaluation screenshots, and its most revealing detail is the unfiltered chain of thought. The build carries the internal identifier models/deepthink-mathematica-tf-raw-thoughts — the "raw thoughts" suffix is the point — with a on

Bilibili opens a 100-model arena — GPT-6 Astra takes the top slot

The Frontier

Bilibili opens a 100-model arena — GPT-6 Astra takes the top slot

Two stories where the ranking comes from outside the lab: China's biggest video platform just turned creator reviews into a live model leaderboard, and a clinical voice company published the first benchmark of whether AI can actually say a drug's name. Bilibili's new AI Infinite Arena ranks models by how often they win — not by how well they score. The platform opened a leaderboard fed by its UP hosts (creators), who test more than a hundred models on their own terms: code, reasoning, collabora

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