Opus 4.7's New Tokenizer Inflates Text Costs ~40% at Same Sticker Price

Simon Willison extended his Claude Token Counter tool to compare token counts across model versions, surfacing a concrete cost implication of Anthropic’s updated tokenizer in Opus 4.7. Anthropic documented the change as a 1.0–1.35x inflation depending on content type, but Willison’s test on the Opus 4.7 system prompt produced a 1.46x ratio against Opus 4.6 — above the stated range.

Pricing per million tokens is unchanged between 4.6 and 4.7 ($5 input, $25 output), so the tokenizer shift translates directly into roughly 40% higher real-world spend for equivalent text payloads. Other content types scale differently: a 15MB, 30-page PDF came in at only 1.08x, suggesting the multiplier is heaviest on raw prose.

Image handling is a separate story. An initial 3.01x jump on a 3.7MB photo looked alarming until Willison retested at lower resolution and saw parity (314 vs 310 tokens). The inflation on large images reflects Opus 4.7’s expanded support for inputs up to ~3.75 megapixels — more than triple the prior ceiling — not a per-pixel cost hike.