AI Desk · AI FingerprintingNew arrival
Why high: an exact fingerprint shared with 1 model that declares the same family, without a second signal of a different kind yet.
Anthropic: Claude Sonnet 5.5 is Anthropic's model. Its measured tokenizer sits with the Claude group, which is evidence that it builds on the Claude tokenizer. Tokenizer reuse is normal engineering, open vocabularies travel between labs, and this says nothing against Anthropic's authorship of the model itself.
| We checked | What we found | Where it came from |
|---|---|---|
| How it counts tokens | Counts every one of the 50 test strings exactly like 1 other model | tk_310f7ba9 |
| How its API is set up | Set up identically to 3 other listings, field for field | api_2aa953b6 |
| How much it can read and write | Reads up to 1,000,000 tokens at once, writes up to 128,000 | its own listing |
| Whether it thinks before answering | Always reasons, and cannot be turned off, at max, xhigh, high, medium, low, high by default | its own listing |
| Who served our requests | Claude Platform on AWS | we measured it, 5 October 2026 |
Click a row to open the full comparison.
We sent Anthropic: Claude Sonnet 5.5 fifty short pieces of text and recorded what each one cost it in tokens. The bars below are those costs. Two models built on the same tokenizer produce the same bars; a model built on a different one produces a different set, which is what makes this a fingerprint.
Overhead subtracted: 8 prompt tokens.
Claude Sonnet 5.5 is Anthropic's Sonnet-class model for well-scoped everyday work, succeeding Claude Sonnet 5 as a direct upgrade. It is especially strong at building features, fixing bugs, and producing...
Supported parameters
include_reasoningmax_completion_tokensmax_tokensreasoningreasoning_effortresponse_formatstopstructured_outputstemperaturetool_choicetoolsverbosity
defaults: {}
