GPT-6.1 and Sonnet 5.5 Released the Same Week

Melvin Vivas · X post · 2026-09-30 · Open on X

Topics: Industry Trends & Job Market, LLM Fundamentals · Level: beginner

Summary

Industry news: GPT-6.1 and Sonnet 5.5 came out in the same week. Both are new frontier models worth looking up and comparing.

GPT-6.1 (OpenAI) and Sonnet 5.5 (Anthropic) were released in the same week, late September 2026.
Two frontier releases at once is a good reason to re-check which model you use for your workloads.

GPT-6.1 Sol · tool · openai.com · paid
A new OpenAI model announced at DevDay 2026 (name as written in the machine transcript), offered with Fast and Ultra fast speed tiers.
Also in: JevDev: Open-Source UI Tool for Experimenting with Jev (Typesafe.ai) (Melvin Vivas on X · notes), Comparing Coding Models on the Same Task in Devin iOS (Melvin Vivas on X · notes), Customizing Your Coding Setup with Pi Coding Agent Extensions (Melvin Vivas on X · notes), Pi Agent Council: Ask Multiple LLMs in Parallel and Compare Their Advice (Melvin Vivas on X · notes) and 9 more
Claude Sonnet 5.5 · tool · anthropic.com · paid
Anthropic's newly released mid-tier Claude model, reported to be strong at agentic coding.
Also in: Generating a Repo Promo Video with a Claude Skill on Sonnet 5.5 vs Opus 5.5 (Melvin Vivas on X · notes), Customizing Your Coding Setup with Pi Coding Agent Extensions (Melvin Vivas on X · notes), Use Sonnet 5.5 instead of Opus 5.5 for faster video-clipping tasks (Melvin Vivas on X · notes), Advisor/Executor setup in Claude Code: Opus 5.5 plans, Sonnet 5.5 runs (Melvin Vivas on X · notes) and 2 more