AI Sec Watch: A Security Intelligence Platform for AI Systems

Luu, T.J.

Opus 4.6 and Codex 5.3

infonewsLLM-Specific

industry

Source: Simon Willison's WeblogFebruary 5, 2026

Summary

Anthropic released Opus 4.6 and OpenAI released GPT-5.3-Codex (currently available only through the Codex app, not via API) as major new model releases. While both models perform well, they show only incremental improvements over their predecessors (Opus 4.5 and Codex 5.2), with one notable demonstration being the ability to build a C compiler (a program that translates code into machine instructions) using multiple parallel instances of Claude working together.

Classification

Attack SophisticationModerate

AI Component TargetedModel

Affected Vendors

AnthropicOpenAI

Related Issues

high

Anthropic accuses Chinese AI labs of mining Claude as US debates AI chip exports

Same vendorTechCrunch

info

Anthropic doesn’t trust the Pentagon, and neither should you

Same vendorThe Verge (AI)

Original source: https://simonwillison.net/2026/Feb/5/two-new-models/#atom-everything

First tracked: February 12, 2026 at 02:28 PM

Classified by LLM (prompt v3) · confidence: 85%