December 2025 sponsors-only newsletter

2026-01-02 · Source: Simon Willison's Weblog · Field: Technology & Digital — Artificial Intelligence & Machine Learning, Emerging Technologies & Innovation, Software Development & Engineering · Depth: Intermediate, quick

Summary

The December 2025 edition of a sponsors-only monthly newsletter, released on January 2, 2026, provides an in-depth review of Large Language Models (LLMs) in 2025. Key topics covered include the author's coding agent projects during December, an overview of new models released in December 2025, and a discussion on "Skills" becoming an open standard. The newsletter also features an analysis of Claude's "Soul Document" and details the tools the author is currently utilizing. Access to this content is available to sponsors, who can subscribe for $10 per month to receive it a month ahead of the free public release.

Key takeaway

For AI Engineers and researchers tracking the rapid evolution of LLMs, subscribing to this newsletter offers early access to critical insights. You can stay a month ahead on new model releases, coding agent project updates, and significant industry developments like "Skills" as an open standard. Consider the $10/month sponsorship to inform your strategic planning and maintain a competitive edge.

Key insights

A monthly newsletter offers early access to LLM trends, coding agent projects, and new model insights for sponsors.

In practice

• Review LLM developments from 2025.
• Explore new models released in December 2025.
• Examine Claude's "Soul Document" concept.

Topics

• Large Language Models
• AI Agents
• Claude AI
• AI Models
• Open Standards

Code references

• sponsors/simonw
• simonw-private/monthly

Best for: AI Engineer, Machine Learning Engineer, Prompt Engineer

Related on AIssential

• The last six months in LLMs in five minutes — LLM capabilities, particularly coding agents and local models, advanced rapidly from November 2025 to April 2026, marked by frequent "best" model shifts.
• April 2026 newsletter — The latest sponsor newsletter details new LLM releases, price changes, and security research.
• Our holiday gift for builders disappears at the new year. — Building production LLM systems requires both foundational design principles and practical engineering for reliable deployment.
• Claude Code Heading for a $100 Paywall Instead of $20! The New Pricing Reality for AI Coding Agents — Advanced AI coding agent services are shifting from flat-rate, low-cost subscriptions to higher-priced tiers due to increased compute demands.
• This Week in AI — AI advancements are rapidly commoditizing capabilities while enabling new forms of automation and creative expression.
• An Open Course on LLMs, Led by Practitioners — Industry veterans offer a free, applied LLM survey course covering evals, RAG, and fine-tuning for technical professionals.

Open in AIssential →

Editorial summary, takeaway, and curation by AIssential. Original article published by Simon Willison's Weblog.