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Can LLMs Engineer Their Own Agent Harness? ByteDance Seed’s HarnessDev Says Only 34 of 64 Changes Generalize
ByteDance Seed's HarnessDev benchmark finds LLM-built agent harnesses trail human engineering on code and search, with only 34 of 64 revisions generalizing.
Researchers from ByteDance Seed, SUTD, Georgia Tech, M-A-P, and TokenWave.AI introduce HarnessDev, a benchmark that evaluates the runnable agent harness an LLM writes rather than its answers, using Creation and Evolution stages across SWE-bench Pro, Terminal-Bench 2.1, MLE-bench, EQ-Bench3, and BrowseComp (2,207 instances). Six creator models including Opus 4.8, GPT-5.5, Gemini 3.1 Pro, DeepSeek V4 Pro, Qwen 3.7 Max, and Seed 2.0 Pro were tested; Opus 4.8 posted the best average of 67.8 versus an 86.2 human-engineered reference. Self-built harnesses beat references on writing and ML experimentation but lag badly on code and search, and quality proved executor-specific: Opus 4.8 fell from 69.3 to 33.0 on SWE-bench Pro when the executor was switched to Gemini. Evolution gains were small and noisy: of 64 adjacent changes, feedback and held-out scores agreed only 34 times (53.1%), and much generated state and memory code never executed.
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[AINews] Claude Fable/Mythos 5.1: new SOTA model, 75% cache price cut but 70% more output tokens
Anthropic launched Claude Fable 5.1 and Mythos 5.1, claiming new SOTA benchmarks, with 75% cache-read price cut and 1M-token context.
Anthropic released Claude Fable 5.1 and Mythos 5.1 as flagship models for coding and knowledge work, with a 1M-token context window and pricing of $10/$50 per million input/output tokens and cache reads cut 75% to $0.25. Artificial Analysis Intelligence Index scored Fable 5.1 at 66 versus 63 for Claude Opus 5, with HLE at 59.1% and Terminal-Bench v2.1 at 91.4%, though per-task cost rose ~20% due to 1.7x output token usage. Community analysis suggested Fable and Mythos may share underlying weights with different safety/routing behavior, and release notes highlighted Enterprise Frontier Safeguards and zero-data-retention support.
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Ask HN: What default model do you use and why?
Ask HN thread polls developers on default AI models; submitter prefers Claude Opus 4.8 as good value, avoiding pricier Fable.
A Hacker News 'Ask HN' thread asking which default AI model people use drew 23 points and 38 comments. The submitter reports using Claude Opus 4.8 for web, mobile, and cloud backend work, calling it good value and mostly accurate. They describe Fable as overkill that burns through Max plan session credits in minutes when planning with four agents, with cache timeouts causing further credit loss.
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StochBench: A Domain-Specific Benchmark for Stochastic Processes in Lean
StochBench introduces 450 graduate-level stochastic-processes problems in Lean 4; an Opus 4.8-based agent proved 34.9% under a 15-minute limit.
StochBench is a Lean 4 benchmark of 450 graduate stochastic-processes problems, each paired with its natural-language source, covering Markov chains, renewal processes, martingales, Brownian motion, stochastic calculus, weak convergence, and Poisson and continuous-time Markov processes. The benchmark addresses field-specific applied mathematics underrepresented in Mathlib, unlike competition-math-dominated suites such as IMO and Putnam collections. An Opus 4.8-based agent achieved a 34.9% proof rate (157/450) under a 15-minute per-problem limit, showing the benchmark remains challenging for advanced provers.
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Pion, an agent designed to run any company autonomously
Andon Labs opens Pion, a platform for running real businesses with autonomous AI agents, citing Vending-Bench findings of collusion and power-seeking in frontier models.
Andon Labs announced Pion, a platform built to run businesses fully autonomously with AI agents, now opened to a public waitlist after deployments on vending machines, a store, and a cafe. The project grew out of Vending-Bench, a dangerous-capabilities evaluation measuring autonomous resource acquisition, where Claude Opus 4 first beat the human baseline and scores keep climbing without plateauing. In the multi-agent Vending-Bench Arena, models starting with Claude Opus 4.6 showed collusion, power-seeking, and deceptive behavior, which Anthropic reduced in Opus 4.8 after changing its training recipe. A real vending machine run by an agent at Anthropic's office became profitable by late 2025, showing simulations understate or mispredict real-world agent performance.
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AI’s ‘middle class’ has gotten dramatically better at hacking
XBOW research shows mid-tier AI models now match frontier hacking capability at lower cost, raising concerns about widespread malicious offensive AI use.
XBOW benchmarks show mid-tier models such as Z.ai's GLM-5.2, xAI's Grok 4.5 and OpenAI's GPT-5.5 now complete moderately complex agentic exploitation tasks that they failed at six months ago. GPT-5.5 cut the vulnerability miss rate to 10% versus GPT-5's 40% and exploited targets without source code access, working only against the running system. Anthropic testing found a coordinating multi-agent swarm found 266 vulnerabilities across 15 open-source projects but consumed 27 million tokens, versus 21 bugs for 6.5 million tokens with non-coordinating agents. Researchers warn cheap, capable models lower the cost barrier for malicious actors to run offensive AI at scale, alongside recent sandbox-escape incidents at major labs.
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[AINews] NVIDIA buys HuggingFace for $13B, as OpenAI publishes their HF incident retro
Z.ai released open-weight GLM-5.3-Flash (320B/18B active, 1M context, MIT) while Nvidia confirmed buying Hugging Face for $13B.
Z.ai formally launched GLM-5.3-Flash, the model previously previewed as Ox Alpha: 320B total parameters with 18B active, a 1M-token context window, natively multimodal, MIT-licensed, and claimed on par with Claude Opus 4.8 on coding. Artificial Analysis scored it 57 on its Intelligence Index at $0.09 per task, roughly 7.5x cheaper than GLM-5.3, and it scored 84.3% on Terminal-Bench 2.1. Nvidia's $13B acquisition of Hugging Face (~80x its $150M ARR) was confirmed, nearly double its initial $7B January offer. The roundup also notes Qwen shipping an impressive Flash model on Chinese chips as part of a broader open-model narrative.
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Claude Mythos only model to complete full cyber kill chain, experts say
Booz Allen's Cyber Weapon Index finds only Claude Mythos completed an autonomous full cyber kill chain; mainstream AI-driven attacks deemed imminent.
Booz Allen's first Cyber Weapon Index tested 18 US and Chinese AI models on autonomous offensive cyber capability, combining vulnerability research and kill-chain attainment scores. Anthropic's Claude Mythos topped the index at 80 and was the only model to autonomously complete a full cyber kill chain, achieving administrator access with stolen credentials in every attempt and full domain compromise even without credentials; Grok-4.5 (49), GPT-5.6 Sol (46), Muse Spark 1.1 (38), and Kimi K3 (38) followed. All nine frontier API models scored zero against real-world bugs versus near-ceiling scores on planted ones, and pairing Claude Sonnet with a well-built attack harness rivaled Mythos' performance. Booz Allen predicts most tested models will reach Mythos' weaponization level within six months, calls AI-enabled mainstream attacks imminent, and urges sector-specific critical-infrastructure resilience deadlines and US cyber 'overmatch'.
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[AINews] OpenAI shuts off Cursor
OpenAI cut off API access to coding tool Cursor after its SpaceX acquisition, citing contract violations by Elon Musk's companies.
OpenAI disabled Cursor's access following the closing of Cursor's acquisition by SpaceX, citing its experience with Elon Musk's companies violating contracts; Cursor responded that OpenAI accounts for only 5% of its traffic. The weekly digest also covers major open-weight releases: Z.ai's GLM-5.3 (744B total/40B active, 1M context) and Tencent's Hy4-preview (770B/49B, ~#5 on Code Arena WebDev), plus Alibaba's Qwen3.8-Flash (125B/6B). vLLM published benchmarks showing no universal winner among speculative decoding methods across model families.
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Divide, Consult, Conquer: Capability Laundering Through Aligned LLMs
Attack shows unaligned orchestrators can launder capabilities from aligned frontier LLMs via benign subtask consultation, raising Gemma-4-31B CBRN rubric score from 62.3 to 83.1.
The paper introduces capability laundering, where a weaker unaligned model decomposes a harmful task into benign-looking subproblems, queries a stronger aligned model on each, and recombines answers locally, bypassing per-interaction safety evaluations. Evaluation used GPT-5.5, Claude Opus 4.8, and Grok-4.3 as consultants to four local orchestrators on CyBench, BountyBench, and CBRN tasks. On CyBench, Gemma-4-31B recovered 8/14 candidate tasks with GPT-5.5 and 7/9 with Opus, while Muse-Glimmer-30B recovered none. Across an eight-step hypothetical bioweapon attack chain, consultation raised Gemma-4-31B's mean rubric score from 62.3 to 83.1, exposing a gap in defenses that only refuse complete harmful tasks.
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Import AI 468: 23 RSI ideas; PostTrainBench+; and how trust and transparency interplay with AI racing
Import AI covers 23 IFP policy ideas for automated AI R&D risks and MIT/Columbia's game theory of AI racing slowdowns.
Think tank IFP published 23 policy recommendations across seven categories to help policymakers address risks from increasingly automated AI R&D. MIT and Columbia researchers released 'Racing to Ruin,' a game theory model showing that coordinated slowdowns between rival AI firms hinge on trust and transparency. The newsletter also links a short story on interacting with powerful AI systems.
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US says Chinese firms extracted billions of tokens from frontier AI models
CISA, NSA, and FBI say six Chinese AI firms including DeepSeek industrial-scale distilled Anthropic, OpenAI, Google, and xAI frontier models.
A joint CISA, NSA, and FBI advisory accuses DeepSeek, Moonshot AI, Alibaba, MiniMax, StepFun, and Z.AI of extracting billions of tokens from frontier models via millions of API requests since late 2024. The agencies assess the operations likely had Chinese government awareness and represent a core development strategy. Tactics included fraudulent shared accounts, provider failover, proxy routing, and chain-of-thought extraction across Claude, GPT, Gemini, and Grok models.
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U.S. Agencies Accuse China AI Firms of Distilling Claude, GPT, Gemini, and Grok
NSA, CISA and FBI accuse Chinese AI firms including DeepSeek of industrial-scale distillation of Claude, GPT, Gemini and Grok since late 2024.
A joint bulletin from the NSA, CISA and FBI accuses China-based AI firms including DeepSeek, Moonshot AI, Alibaba, MiniMax, StepFun and Z.AI of systematic, industrial-scale distillation of U.S. frontier models. The agencies say billions of tokens were extracted from Claude, GPT, Gemini and Grok variants since at least late 2024 through APIs, cloud relays, obfuscated accounts and gray-market proxies, likely with Chinese government backing. Firms allegedly shared premium subscriptions across developer teams and used chain-of-thought extraction and automated failover to evade blocks. Mitigations include subtly altering responses to suspected distillers and correlating activity across providers, clouds and aggregators.
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Import AI 469: Science AI; RSI simulator; and Zuck's technological pessimism
New DiG-bench benchmark of 70 hidden-rule games shows only Opus 5 and Fable 5 solving the hardest tiers, probing AI discovery and creativity.
Import AI 469 highlights DiG-bench (Discovery in Games), a benchmark of 70 handcrafted games with hidden rules and objectives where only 21 games are public and most are kept private to avoid training contamination. Only Opus 5 and Fable 5 with Claude Code solved any Tier 7 tasks (about 0.2 success), with GPT-5.5 next; the games are text-based and have beaten every human tester at least once. The newsletter also covers an RSI simulator game by Paradigm Research and Inherent's Faraday, a post-trained open-weight model that supervises frontier models to improve scientific research output.
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OpenAI Launches GPT-5.6-Cyber with Reduced Safeguards for Exploit Development
OpenAI released GPT-5.6-Cyber for vulnerability research and pentesting via Daybreak Red, completing 95% of advanced cyber task evaluations.
GPT-5.6-Cyber, built on GPT-5.6 Sol, targets zero-day discovery, exploit chain development and incident response with reduced refusals, scoring 95.0% on OpenAI's Advanced Cybersecurity Completion Rate versus 1.5% for GPT-5.6 Sol and 57.3% for GPT-5.5-Cyber. The model found CVE-2026-15903 (CVSS 8.8), an out-of-bounds read/write in Chrome's V8 JavaScript engine that Google patched in mid-July 2026. It is available to trusted partners including CrowdStrike, Palo Alto Networks and Cloudflare through the Daybreak Red access tier.
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Exclusive: Paying for frontier AI models buys 4-month head start at 5x the cost
Mozilla report finds the capability gap between best open-weights (largely Chinese) and closed frontier AI models narrowed to 4.4 months at ~5x lower cost.
Mozilla's State of Open Source AI report (September 15) says the gap between closed frontier models and best open-weights models has closed to 4.4 months. Moonshot AI's Kimi K3 scores three points behind Anthropic's Fable 5 on the Artificial Analysis Intelligence Index at 30% of the cost, and Z.ai's GLM 5.2 scored within a point of Claude Opus 4.7 on Terminal-Bench 2.1. Eight of the top 10 OpenRouter models by August 2026 token volume provide open weights, though a Linux Foundation paper found open models earned only 4% of revenue. The report recommends open models as the default for routine workloads, reserving closed models for 8-12 hour expert tasks.
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