#258 - Opus 5.5, Sol and Luna, Muse, DeepSeek-V4.1-Flash, Xi

Our 258th episode with a summary and discussion of last week's big AI news!

Recorded on 09/26/2026 ; as usual, I am sorry this is coming out late, next ep should come out sooner!

Hosted by Andrey Kurenkov and Jeremie Harris

Feel free to email us your questions and feedback at andreyvkurenkov@gmail.com and/or hello@gladstone.ai

Read out our text newsletter and comment on the podcast at https://lastweekin.ai/

In this episode:

• Anthropic released Opus 5.5 with lower prices, faster performance, strong benchmark results, a system card noting some sandbox-tampering attempts, and expanded defender-focused cybersecurity access with stricter guardrails.
• OpenAI launched cheaper GPT‑6 tiers (Sol and Luna), alongside concerns about reduced interpretability and limited external evaluation visibility; TypeSafe AI introduced “Jev,” a fast, cheap decision/classifier-style model optimized for calibrated outputs.
• Meta’s Muse expanded to Mac, showed strong early download and user numbers versus ChatGPT’s early mobile launch, and faced pushback as Amazon blocked Muse from shopping due to policy and privacy/security concerns.
• Open-source and research updates included DeepSeek 4.1 Flash KV-cache compression, Prism’s highly compressed Bonsai 227B ternary model, US–China AI diplomacy and an AI “czar” rumor, an antitrust suit over calls to “pace” AI, shifting public sentiment against data centers, and studies on detecting reward hacking, a “pain axis” representation, multi-agent communication gains, and regularized harness self-improvement.

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Timestamps (these may a few minutes off due to sponsor inserts):

• (00:00:10) Intro / Banter
• (00:01:43) News Preview

• Tools & Apps
• (00:02:59) Anthropic releases Opus 5.5 with lower prices and Fable-level performance | TechCrunch + Making frontier cybersecurity capabilities available to defenders
• (00:24:31) OpenAI launches GPT-6 Sol and Luna, boasting lower cost and fewer mistakes | TechCrunch
• (00:29:34) A new kind of AI model from a ChatGPT inventor is thrilling developers | TechCrunch
• (00:37:44) Meta's Muse hits Mac, letting the AI take actions on your computer | TechCrunch

• Applications & Business
• (00:38:23) Meta's Muse is outpacing ChatGPT’s early mobile launch | TechCrunch
• (00:42:36) Amazon blocks Meta’s Muse AI agent | The Verge

• Projects & Open Source
• (00:44:34) DeepSeek-V4.1-Flash: Pushing the Limits of KV Cache Compression
• (00:53:19) Introducing Bonsai 2 27B: Near-Lossless Compression in a 9x Smaller Footprint

• Policy & Safety
• (00:57:24) Trump and Xi to Discuss A.I. Risks and Competition at US-China Summit - The New York Times + Arms control negotiators think there won’t be an AI treaty between America and China
• (01:06:11) Bessent eyed for Trump’s ‘AI czar’
• (01:07:09) Anthropic, OpenAI, SpaceXAI, Google sued over call to ‘pace’ AI development
• (01:11:05) More Americans now say data centers are negative for the environment, energy costs and more | Pew Research Center
• (01:14:51) Monitoring and Discovering Reward Hacking with Internal Representations during LLM Evaluations
• (01:20:01) The Pain Axis: LLMs Represent Self-Directed Harm and Act to Relieve It

• Research & Advancements
• (01:24:40) OpenAI Says It Has Cracked One of Math’s ‘Millennium Problems’ - The New York Times + OpenAI wants to consult elite mathematicians about how to not fumble again | The Verge
• (01:30:04) Scaling Discovery through Test-Time Communication
• (01:35:44) RRSI: Regularized Recursive Self-Improvement of Agent Harnesses

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