Claude Token Counter adds cross-model comparisons; Opus 4.7 shows big token inflation

Claude Token Counter — Simon Willison’s handy little tool for measuring how many tokens models eat — now lets you run the same input across multiple Claude models for side‑by‑side comparisons. It has been reported that the tool supports Opus 4.7 and 4.6, Sonnet 4.6, and Haiku 4.5, making it easy to spot differences in tokenization and cost implications. Simple, useful, and the kind of thing you wish you had before your credit card bill arrived.

What changed under the hood

Anthropic announced that Opus 4.7 uses an updated tokenizer that "improves how the model processes text" and warned that the same input can map to roughly 1.0–1.35× more tokens depending on content. But it has been reported that Willison’s tests show even larger jumps: pasting the Opus 4.7 system prompt into the counter produced about 1.46× the tokens of Opus 4.6. Ouch. That’s not a rounding error — it’s a real, measurable difference in how text is broken up.

Images and the sticker shock

The token counter also accepts images, and Opus 4.7 claims better high‑resolution vision — up to 2,576 pixels on the long edge (roughly 3.75 megapixels), more than three times prior models. It has been reported that Willison’s test PNG (3.7MB, 3456×2234) returned a 3.01× token count for 4.7 versus 4.6. That’s the kind of surprise that makes you squint at your deployment plan. Anthropic keeps pricing for Opus 4.7 the same as Opus 4.6 — $5 per million input tokens, $25 per million output tokens — but it has been reported that token inflation like this could push real costs substantially higher (Willison estimates roughly a 40% increase in some cases).

Why it matters

Want accuracy or better image handling? Opus 4.7 might be worth the extra spend. Want to keep costs predictable? You’ll want to test aggressively. Tools like the upgraded Claude Token Counter make that testing trivial — and remind us that model upgrades can be a mixed bag: better understanding, bigger bills. Who knew tokenizer tweaks could feel like inflation?

Sources: simonwillison.net, Hacker News