Anthropic shipped claude 4.5 the same day openai pushed codex upgrades and four days after gpt-6…
anthropic shipped claude 4.5 the same day openai pushed codex upgrades and four days after gpt-6 astra dropped. three frontier releases in one week, every team i know still has the previous version pinned.
the eval window just collapsed to less than a release cycle.
Context
No Anthropic release named Claude 4.5 was found on or around the date of the note. Anthropic's pages describe the Claude 4.5 family as Opus 4.5, Sonnet 4.5 and Haiku 4.5, with Sonnet 4.5 released on 29 September 2025. Anthropic's September 2026 release in the sources read was Claude Fable 5.1 and Mythos 5.1 on 1 September 2026.
The exact version and date the note refers to are unverified, and no other model name is substituted for it. The interval after GPT-6 Astra depends on the anchor: OpenAI's own dates are 1 September 2026 for Path to Astra and 3 September 2026 for the system card and rollout. No same-day evidence for the Codex upgrades was inspected. The previous version still pinned and the eval window collapsing are the author's opinion.
Related work
- Claude Sonnet 4.5 (Anthropic) ↗Dated 29 September 2025; snippet only.
- Claude models overview (Anthropic docs) ↗Snippet only.
Watch next
- The Anthropic release the note refers to, if located.
Sources
- Claude Fable and Mythos 5.1 (Anthropic)anthropic.com
- Claude Haiku 4.5 system prompt release notes (Anthropic docs)platform.claude.com
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 5 September 2026 at 23:17 IST. Sources are the papers and datasets the note draws on.
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