LessWrong posts by zvi

OpenAI is back with a new Codex model, released the same day as Claude Opus 4.6.

The headline pitch is it combines the coding skills of GPT-5.2-Codex with the general knowledge and skills of other models, along with extra speed and improvements in the Codex harness, so that it can now handle your full stack agentic needs.

We also got the Codex app for Mac, which is getting positive reactions, and quickly picked up a million downloads.

CPT-5.3-Codex is only available inside Codex. It is not in the API.

As usual, Anthropic's release was understated, basically a ‘here's Opus 4.6, a 212-page system card and a lot of benchmarks, it's a good model, sir, so have fun.’ Whereas OpenAI gave us a lot less words and a lot less benchmarks, while claiming their model was definitely the best.

OpenAI: GPT-5.3-Codex is the most capable agentic coding model to date, combining the frontier coding performance of GPT-5.2-Codex with the reasoning and professional knowledge capabilities of GPT-5.2. This enables it to take on long-running tasks that involve research, tool use, and complex execution.

Much like a colleague, you can steer and interact with GPT-5.3-Codex while [...]
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Outline:
(01:50) The Overall Picture
(03:00) Quickly, Theres No Time
(04:15) System Card
(04:49) AI Box Experiment
(05:22) Maybe Cool It With Rm
(07:02) Preparedness Framework
(11:14) Glass Houses
(12:16) OpenAI Appears To Have Violated SB 53 In a Meaningful Way
(14:29) Safeguards They Did Implement
(16:55) Misalignment Risks and Internal Deployment
(18:38) The Official Pitch
(24:28) Inception
(26:12) Turn The Beat Around
(27:35) Codex Does Cool Things
(29:33) Positive Reactions
(38:03) Negative Reactions
(40:43) Codex of Ultimate Vibing
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First published:

February 13th, 2026


Source:

https://www.lesswrong.com/posts/CCDRjL7NZtNGtGheY/chatgpt-5-3-codex-is-also-good-at-coding

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Life comes at you increasingly fast. Two months after Claude Opus 4.5 we get a substantial upgrade in Claude Opus 4.6. The same day, we got GPT-5.3-Codex.

That used to be something we’d call remarkably fast. It's probably the new normal, until things get even faster than that. Welcome to recursive self-improvement.

Before those releases, I was using Claude Opus 4.5 and Claude Code for essentially everything interesting, and only using GPT-5.2 and Gemini to fill in the gaps or for narrow specific uses.

GPT-5.3-Codex is restricted to Codex, so this means that for other purposes Anthropic and Claude have only extended the lead. This is the first time in a while that a model got upgraded while it was still my clear daily driver.

Claude also pulled out several other advances to their ecosystem, including fast mode, and expanding Cowork to Windows, while OpenAI gave us an app for Codex.

For fully agentic coding, GPT-5.3-Codex and Claude Opus 4.6 both look like substantial upgrades. Both sides claim they’re better, as you would expect. If you’re serious about your coding and have hard problems, you should try out both, and see what combination works [...]
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Outline:
(01:55) On Your Marks
(17:35) Official Pitches
(17:56) It Compiles
(21:42) It Exploits
(22:45) It Lets You Catch Them All
(23:16) It Does Not Get Eaten By A Grue
(24:10) It Is Overeager
(25:24) It Builds Things
(27:58) Pro Mode
(28:24) Reactions
(28:36) Positive Reactions
(42:12) Negative Reactions
(50:40) Personality Changes
(56:28) On Writing
(59:11) They Banned Prefilling
(01:00:27) A Note On System Cards In General
(01:01:34) Listen All Yall Its Sabotage
(01:05:00) The Codex of Competition
(01:06:22) The Niche of Gemini
(01:07:55) Choose Your Fighter
(01:12:17) Accelerando
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First published:

February 11th, 2026


Source:

https://www.lesswrong.com/posts/5JNjHNn3DyxaGbv8B/claude-opus-4-6-escalates-things-quickly

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Coverage of Claude Opus 4.6 started yesterday with the mundane alignment and model welfare sections of the model card.

Today covers the kinds of safety I think matter most: Sabotage, deception, situational awareness, outside red teaming and most importantly the frontier, catastrophic and existential risks. I think it was correct to release Opus 4.6 as an ASL-3 model, but the process Anthropic uses is breaking down, and it not on track to reliably get the right answer on Opus 5.

Tomorrow I’ll cover benchmarks, reactions and the holistic takeaways and practical implications. I’m still taking it all in, but it seems clear to me that Claude Opus 4.6 is the best model out there and should be your daily driver, with or without Claude Code, on most non-coding tasks, but it is not without its weaknesses, in particular in writing and falling into generating more ‘AI slop’ style prose than Claude Opus 4.5.

For coding tasks, I presume that Opus 4.6 with Claude Code is the play, especially with Agent Teams and fast mode available, and I’m using it myself, but Codex with GPT-5.3-Codex-Max is also a strong model and a viable alternative, and a fully [...]
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Outline:
(01:32) Sabotage, Deception and Evaluation Integrity
(03:42) Sandbagging On Dangerous Capability Evaluations
(06:01) Situational Awareness
(07:33) Inhibiting Evaluation Awareness (6.5)
(09:06) Self-Preference
(10:24) UK AISI Testing
(11:40) Apollo Research Testing
(14:24) Responsible Scaling Policy Evaluations
(15:45) CBRN (mostly Biology)
(18:43) Autonomy
(26:40) Autonomy Benchmarks
(29:53) Cyber
(31:27) Ship It Anyway
(33:40) You Are Not Ready
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First published:

February 10th, 2026


Source:

https://www.lesswrong.com/posts/togCQtFtfdF23xGNS/claude-opus-4-6-system-card-part-2-frontier-alignment

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Claude Opus 4.6 is here. It was built with and mostly evaluated by Claude.

Their headline pitch includes:


1M token context window (in beta) with State of the art retrieval performance.

Improved abilities on a range of everyday work tasks. Model is improved.

State of the art on some evaluations, including Terminal-Bench 2.0, HLE and a very strong lead in GDPval-AA.

Claude Code now has an experimental feature called Agent Teams.

Claude Code with Opus 4.6 has a new fast (but actually expensive) mode.

Upgrades to Claude in Excel and the release of Claude in PowerPoint.

Other notes:


Price remains $5/$25, the same as Opus 4.5, unless you go ultra fast.

There is now a configurable ‘effort’ parameter with four settings.

Refusals for harmless requests with rich context are down to 0.04%.

Data sources are ‘all of the above,’ including the web crawler (that they insist won’t cross CAPTCHAs or password protected pages) and other public data, various non-public data sources, data from customers who opt-in to that and internally generated data. They use ‘several’ data filtering methods.

Thinking mode gives better [...]
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Outline:
(03:45) A Three Act Play
(04:57) Safety Not Guaranteed
(10:53) Pliny Can Still Jailbreak Everything
(12:48) Transparency Is Good: The 212-Page System Card
(13:53) Mostly Harmless
(17:45) Mostly Honest
(19:01) Agentic Safety
(20:27) Prompt Injection
(23:07) Key Alignment Findings
(33:48) Behavioral Evidence (6.2)
(38:40) Reward Hacking and 'Overly Agentic Actions'
(40:37) Metrics (6.2.5.2)
(42:40) All I Did It All For The GUI
(43:58) Case Studies and Targeted Evaluations Of Behaviors (6.3)
(44:19) Misrepresenting Tool Results
(45:09) Unexpected Language Switching
(46:12) The Ghost of Jones Foods
(47:54) Loss of Style Points
(48:54) White Box Model Diffing
(49:13) Model Welfare
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First published:

February 9th, 2026


Source:

https://www.lesswrong.com/posts/sWsSncqMLKyGZA9Ar/claude-opus-4-6-system-card-part-1-mundane-alignment-and

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Claude Opus 4.6 and agent swarms were announced yesterday. That's some big upgrades for Claude Code.

OpenAI, the competition, offered us GPT-5.3-Codex, and this week gave us an app form of Codex that already has a million active users.

That's all very exciting, and next week is going to be about covering that.

This post is about all the cool things that happened before that, which we will be building upon now that capabilities have further advanced. This if from Before Times.

Almost all of it still applies. I haven’t had much chance yet to work with Opus 4.6, but as far as I can tell you should mostly keep on doing what you were doing before that switch, only everything will work better. Maybe get a bit more ambitious. Agent swarms might be more of a technique shifter, but we need to give that some time.

Table of Contents


Claude Code and Cowork Offer Mundane Utility.

The Efficient Market Hypothesis Is False.

Inflection Point.

Welcome To The Takeoff.

Huh, Upgrades.

Todos Become Tasks.

I’m Putting Together A Team.

Compact Problems.

Code Yourself A [...]
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Outline:
(01:02) Claude Code and Cowork Offer Mundane Utility
(04:07) The Efficient Market Hypothesis Is False
(07:26) Inflection Point
(11:07) Welcome To The Takeoff
(11:29) Huh, Upgrades
(16:02) Todos Become Tasks
(17:46) I'm Putting Together A Team
(20:06) Compact Problems
(20:53) Code Yourself A Date
(24:20) Verification and Generation Are Distinct Skills
(26:07) Skilling Up
(34:12) AskUserQuestion
(34:42) For Advanced Players
(36:53) So They Quit Reading
(37:24) Reciprocity Is The Key To Every Relationship
(41:37) The Implementation Gap
(45:04) The Lighter Side
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First published:

February 6th, 2026


Source:

https://www.lesswrong.com/posts/iwX2aJPKtyKAbLdip/claude-code-4-from-the-before-times

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