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Claude tokenizer counts schema bytes 64% higher than tiktoken, study finds

A recent measurement study by an independent researcher reveals significant discrepancies in how different LLM tokenizers, specifically Claude's and tiktoken, count tokens for the same schema data. The study found that Claude's tokenizer counts schema bytes approximately 64% higher than tiktoken, a widely used offline and free tokenizer. This difference can lead to a substantial overestimation of context window usage when using Claude for tools that rely on schema serialization, potentially impacting cost calculations and effective context window size. The research also highlighted variations in tool exposure and client-side optimizations, such as progressive disclosure in Claude Code, which can drastically reduce the actual token load for end-users. AI

IMPACT Highlights potential cost and context window miscalculations for Claude users, emphasizing the need for accurate tokenizer measurements.

RANK_REASON Independent measurement study comparing LLM tokenizers. [lever_c_demoted from research: ic=1 ai=1.0]

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Claude tokenizer counts schema bytes 64% higher than tiktoken, study finds

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  1. dev.to — MCP tag TIER_1 English(EN) · Roshan Singh ·

    I measured what 14 MCP servers cost a context window. Claude counts them 64% higher than tiktoken

    <p>Last month I <a href="https://dev.to/lopster568/what-should-an-mcp-tool-return-i-ran-72-trials-instead-of-arguing-43b4">ran 72 trials</a> to settle what an MCP tool should return, because a maintainer would not take opinion for an answer. That left the other half open: before …