claude-sonnet-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.
Sonnet 5.5 (claude-sonnet-5-5) is now in the model list and is what sonnet picks when using Anthropic directly
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.284.
In the changelogs
4Releases whose published page names claude-sonnet-5-5.
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v2.1.284
Sonnet 5.5 added and made the default for the
sonnetmodel nameSonnet 5.5 (
claude-sonnet-5-5) is now in the model list and is whatsonnetpicks when using Anthropic directlyfound in this entry's text, named in this entry
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v2.1.284
The sonnet model name now points to Sonnet 5.5 on the Anthropic API
Choosing sonnet now selects Sonnet 5.5 instead of Sonnet 5 on the Anthropic API, while Bedrock, Vertex and other providers keep older models
found in this entry's text, named in this entry
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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
Refused requests on Sonnet 5.5 now fall back to Sonnet 5
When a Sonnet 5.5 request is refused as cyber or frontier_llm, Claude Code now falls back to claude-sonnet-5 instead of an Opus model
found in this entry's text, named in this entry
First cited
6The earliest release whose published evidence quoted claude-sonnet-5-5 was v2.1.284, 28 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.
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.