claude-opus-5-5
A Claude Code model, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
New Opus 5.5 model added with a 1M-token context window and its own pricing tier
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.280.
In the changelogs
20Releases whose published page names claude-opus-5-5.
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v2.1.304
Bundled default model changes to Opus 5.5 at medium effort
The model catalog shipped with Claude Code now defaults to claude-opus-5-5 at medium effort instead of claude-opus-5 at high effort
found in this entry's text
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v2.1.293
Artifact edit shortcut settings are read more strictly and can tag requests
The remote setting for the artifact edit shortcut can now mark its model requests as side replies, and a bad model list now turns it off
found in this entry's text
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v2.1.288
Shortcut for artifact edit requests that skips the model call, built but switched off
Built but off unless enabled remotely: a shortcut that answers some artifact edit requests with direct file edits instead of a model reply
found in this entry's text
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v2.1.284
Claude Code's built-in model list now points to Opus 5.5 and Sonnet 5.5
Claude Code's built-in current models are now claude-opus-5-5 and claude-sonnet-5-5, with claude-opus-5 and claude-sonnet-5 as the previous ones
found in this entry's text
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v2.1.284
Sonnet models get the same safeguard refusal explanations as Opus 5.5
Sonnet sessions now get the "You may be seeing this for the first time" notice on cyber refusals and a recovery option for frontier_llm refusals
found in this entry's text
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v2.1.284
Sonnet models now explain first-time safeguard flags for cyber topics
When safeguards flag a message on a Sonnet model in the cyber category, you now get the first-time explanation that Opus 5.5 already showed
found in this entry's text
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v2.1.283
Opus 5.5 can fall back to Opus 5 for one more refusal type
When claude-opus-5-5 refuses a request in the frontier_llm category, Claude Code can now fall back to claude-opus-5
found in this entry's text, named in this entry
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v2.1.282
Opus 5.5 is now described as "Most capable for ambitious work"
The description for Opus 5.5 in a model list now reads "Most capable for ambitious work" instead of "For complex tasks"
found in this entry's text, named in this entry
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v2.1.282
Opus 5 moved to the overflow section of the built-in model list
In the built-in model list, Opus 5 moves to the overflow section and loses its quick-select flag and description
found in this entry's text
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v2.1.281
Bundled model catalog adds claude-opus-5-5 ("Opus 5.5"), which replaces Opus 5 in the Opus picker slot
Opus 5.5 (
claude-opus-5-5) replaces Opus 5 in the model picker's Opus slot, with default effort "medium" on theccsurfacefound in this entry's text, named in this entry
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v2.1.281
Bundled changelog gains the 2.1.280 entry (Opus 5.5 default)
The release notes built into Claude Code now open with a 2.1.280 section announcing Claude Opus 5.5 as the default Opus model
found in this entry's text, named in this entry
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v2.1.281
Bundled model catalog: 'Opus 5' quick-select entry is now 'Opus 5.5'
In the bundled model catalog, the "Opus" quick-select entry now points to Opus 5.5 instead of Opus 5
found in this entry's text, named in this entry
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v2.1.281
Bundled model-preset config: chat preset thinking effort for claude-opus-5-5 set to medium
A bundled model config now lists claude-opus-5-5 at medium thinking effort for the chat preset, alongside claude-opus-5 at high
found in this entry's text, named in this entry
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v2.1.281
Bundled model-selector sample defaults Opus 5.5 to medium effort
Built-in model data now sets Opus 5.5 to medium effort and marks Medium as Default for Opus 5.5 and Fable 5.1
found in this entry's text
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v2.1.280
Opus 5.5 model added
New Opus 5.5 model added with a 1M-token context window and its own pricing tier
found in this entry's text, named in this entry
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v2.1.280
Fast mode no longer restricted to Opus 5/4.8 in the system prompt
The system prompt no longer says fast mode is limited to Opus 5/4.8, and now lists Opus 5.5 in the model catalog
found in this entry's text, named in this entry
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v2.1.280
Opus renamed to Opus 5.5 as the latest-per-family model
Opus model catalog entry renamed from 'Opus 5' to 'Opus 5.5' as the latest in its family
found in this entry's text
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v2.1.280
Opus 5.5 model reference appears in the model picker UI
The model picker now applies its special styling to "Opus 5.5" instead of "Fable 5.1"
found in this entry's text, named in this entry
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v2.1.280
New 'safeguards flagged' messaging tailored to Opus 5.5
Opus 5.5 gets its own tailored explanation when a message is flagged by safeguards
found in this entry's text
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v2.1.280
New cheaper cost table for claude-opus-5-5
A new, cheaper token-cost tier now applies to the claude-opus-5-5 model id
found in this entry's text, named in this entry
First cited
12The earliest release whose published evidence quoted claude-opus-5-5 was v2.1.280, 22 Sep 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
6 further spans in the ledger name it. The list above is the earliest first and stops at 6.
Presence across releases
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the model does. All models.