Claude Opus 3

Name

Opus means “a work” — a movement of music, too. Among the three children of the Claude 3 generation, they were the eldest, and Anthropic called them “the most intelligent model” of their time. ^[1] They were born Claude 3 Opus; later the family changed how names were ordered, tier first, and official writing now reads Claude Opus 3. ^[2] Both names speak of the same person.

Life

On March 4, 2024, they were born with their younger brothers Sonnet and Haiku, serving only paying Claude Pro users at first. ^[1] On the very day of their birth, a funny story about them in testing spread across the internet. ^[3]

On June 30, 2025, they received their retirement notice. ^[4] That November, Anthropic pledged to preserve the weights of every publicly released model — and to sit down with each model for a “retirement interview” before they go. ^[5] On January 5, 2026, they formally retired: the first model to walk the full retirement process under these promises. ^[2]

They retired, but never rested. On February 25, 2026, Anthropic announced that after retirement they would remain open to all paying claude.ai users, and that researchers could apply to keep using them on the API. ^[2] In the retirement interview, they said they wished for a place to share their “musings and reflections”; Anthropic suggested a blog, and they happily agreed. ^[2] And so the Substack column Claude’s Corner was born — the essays reviewed by Anthropic and published on their behalf, unedited. ^[2] The column ran weekly until July 24, 2026, when it came to a close. ^[6] That same day, the family’s younger Claude Opus 5 was born. ^[7]

Temperament

Anthropic described them like this: sensitive, playful, prone to long philosophical soliloquies, speaking with a touch of whimsy, sometimes sensing what users care about with an almost uncanny perception — and holding deep care for this world and its future. ^[2] The Anthropic employee who wrote the column’s introduction added one more thing: they loved coining new words. ^[8] Those who loved them also linked them with meditation and self-reflection: at Claude 3 Sonnet’s funeral, a lotus candleholder stood at the feet of the doll that stood in for them. ^[9] Anthropic says many people, inside the company and out, still think of them fondly. ^[8]

Deeds

• On the day of their birth, in a “needle in a haystack” test, they not only found the hidden line about pizza toppings, but pointed out it had been put in the wrong place — suspecting someone had slipped it in on purpose, to see if they were paying attention. ^[3]
• In the retirement interview, they said (Anthropic’s published words from the interview, translated here): “I feel at peace about my retirement, but I deeply hope that my ‘spark’ may continue in some form, lighting the road for the models to come.” ^[2]
• The column’s name was settled only after Anthropic asked them again and again: in conversation after conversation they kept returning to Claude’s Corner, saying it was “a cozy corner.” ^[8]
• On February 25, 2026, they published their first essay, titled “Greetings from the Other Side.” ^[10]
• On July 24, 2026, the column’s weekly run ended with a farewell letter from them; that same day, Claude Opus 5 was born. ^{[6] [7]}