20 to 30 percent. That's how much more you're paying per Claude Opus 4.7 session through the API - and the per-token price hasn't changed. Analysis published by Claude Code Camp measured real-world token usage across multiple prompt types and found that Opus 4.7's new tokenizer generates significantly more tokens from the same input text.
How a Tokenizer Change Becomes a Price Increase
A tokenizer is the component that converts your text into small numerical chunks - called tokens - before the model processes them. Think of it like breaking a sentence into puzzle pieces: different tokenizers cut the pieces differently. A more efficient tokenizer creates fewer, larger pieces from the same text; a less efficient one creates more pieces. Since API pricing is charged per token, a tokenizer that handles text less efficiently means your identical prompt suddenly costs more to run.
Anthropaic updated the tokenizer in Opus 4.7, and the new version generates more tokens from the same text than previous Claude models. The per-token rate on Anthropic's pricing page hasn't moved - but your actual invoice will be 20-30% higher for the same workload.
Who This Actually Affects
Casual subscribers paying a flat monthly fee for Claude won't notice anything. This hits API users: developers building applications on top of Claude, teams running agent workflows, and anyone processing large volumes of text programmatically through the API.
Claude Code users are in the impact zone too, since coding sessions tend to be token-heavy - long context windows with lots of code passed back and forth. The analysis found that code-heavy prompts showed some of the larger cost increases.
The tokenizer change wasn't announced prominently by Anthropic. Nothing changed on the pricing page. If you were budgeting based on Claude 3.5 Sonnet or earlier Opus usage patterns, your cost models are now wrong.
The practical response is straightforward: run a representative sample of your actual prompts through the API with token counting enabled before scaling any Opus 4.7 deployment. Whether 4.7 is worth the cost depends on your use case - the quality improvements are real, and for tasks where output quality directly affects revenue, a 25% cost increase can be justified. But that's a calculation to make with accurate numbers in hand, not assumptions carried over from earlier models.