What changed
Anthropic’s Claude account said on 22 September 2026 that Claude Opus 5.5 is available that day. The same post showed an algorithmic drawing program created by @kevin_t_ngo, with every drawing based on a different seed. A seed is a starting number that makes a generative program produce one specific, repeatable picture. The post does not include the program, a seed list, or a repository link.
Claude Code — Anthropic’s coding agent for the terminal and editors — lists the model in its changelog as Claude Opus 5.5 (`claude-opus-5-5`), now the default Opus model. Opus is Anthropic’s higher-capability Claude family. That addition bullet also states a 1M context window and a $4/$20 per Mtok pair, with $0.20/Mtok for cache reads. Mtok is a million tokens. The changelog prints that pair without an input or output label on either side. The drawing program is a creative showcase in Anthropic’s post.
| Term | Changelog text |
|---|---|
| Model id | claude-opus-5-5 |
| Default Opus model | Claude Opus 5.5 |
| Context window | 1M |
| Price pair | $4/$20 per Mtok |
| Cache reads | $0.20/Mtok |
| Plan default (Pro and Team Standard) | Changed from Sonnet to Opus, matching Max, Team Premium, and Enterprise |
Who gets it
The changelog says the default model on Pro and Team Standard plans changed from Sonnet to Opus, matching Max, Team Premium, and Enterprise. Sonnet is Anthropic’s mid-tier Claude family. Anthropic’s X post is silent on which subscriptions receive Opus 5.5.
How to try it
In Claude Code, pick the model with `/model`. On Pro and Team Standard, the changelog says the default is now Opus, matching Max, Team Premium, and Enterprise. Run `claude --version` to check the installed Claude Code version. Effort — how hard the model works on a turn — is set per model with `/effort`. An effort level saved before that change no longer applies to newly released models such as Opus 5.5; they start at their default until you pick a level.
Still unclear
Anthropic’s post ties availability to 22 September 2026. The changelog lists the model id, context window, the $4/$20 per Mtok pair, cache-read rate, and Claude Code plan defaults with no calendar ship date next to those bullets. Whether claude.ai and the API console share those defaults is outside that page.
Source
Also from
Sources and editorial approach
Read the complete @claudeai X post body (published 2026-09-22) and the Claude Code changelog at https://code.claude.com/docs/en/changelog.md. Model id, 1M context, $4/$20 per Mtok, $0.20/Mtok cache reads, the Pro/Team Standard default change, and the /effort migration are taken from changelog bullets on that page. The $4/$20 pair is quoted as printed; the line does not label input versus output. The changelog page is long; a dated version heading for the Opus 5.5 bullets was not visible in the portion used. The page-level `claude --version` line checks the installed Claude Code version. `/model` is named from changelog notes on the model picker. No Claude API model card, pricing page, or claude.ai product page was read. The post does not include the drawing program’s code, seed list, or a repository link.