Claude Token Counter -- Anthropic API Tokens

Claude Token Counter

Claude Token Counter estimates how many tokens your text will use with Claude Opus 4.6, Claude 4.5 Sonnet, and other Anthropic models. Claude uses a proprietary tokenizer that averages about 3.9 characters per token for English text.

Claude Model Comparison

Claude models are organized in three tiers: Haiku (fast/cheap), Sonnet (balanced), and Opus (most capable). All use Anthropic's proprietary tokenizer.

How Claude Tokenization Works

Claude uses a proprietary BPE-based tokenizer developed by Anthropic. Unlike OpenAI's tiktoken, the Claude tokenizer is not available as a standalone open-source library. However, Anthropic provides an API endpoint for exact token counting.

Key Differences from OpenAI

• Proprietary tokenizer: Not publicly available for local use
• Slightly different efficiency: ~3.9 chars/token vs OpenAI's ~4.0 chars/token
• System tokens not billed: Anthropic does not charge for internal system prompt tokens
• Count-tokens API: Free endpoint to get exact token counts before making API calls

Using the Anthropic Count Tokens API

You can get exact token counts using the Anthropic API before making a request:

curl https://api.anthropic.com/v1/messages/count_tokens \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "content-type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-5-20250929",
    "messages": [{"role": "user", "content": "Hello, world!"}]
  }'

This returns the exact token count without generating a response or incurring generation costs.

Frequently Asked Questions

How does Claude count tokens?

Claude uses a proprietary BPE-based tokenizer developed by Anthropic. It is optimized for English text at about 3.9 characters per token, but handles code and multilingual text as well. For exact counts, use the count-tokens API endpoint.

What tokenizer does Anthropic use?

Anthropic uses a proprietary Byte Pair Encoding (BPE) tokenizer. Unlike OpenAI's tiktoken, it is not available as an open-source library. You can get exact counts via the POST /v1/messages/count_tokens API endpoint at no cost.

How much does Claude Opus 4.6 cost?

Claude Opus 4.6 costs $5.00 per million input tokens and $25.00 per million output tokens. It has a 200K standard context window with 1M available in extended beta. It is Anthropic's newest and most capable model (released Feb 5, 2026).

What is the Claude context window?

Most current Claude models have a 200,000 token context window. Claude Opus 4.6 and Claude 4.5 Sonnet also have a 1M token extended context available in beta. This is comparable to GPT-4.1's 1M context and smaller than Gemini's 2M window.

Can I count Claude tokens locally?

Not exactly. Anthropic does not publish their tokenizer as a standalone library. For estimates, use approximately 3.9 characters per token (this tool does that). For exact counts, use the Anthropic count-tokens API endpoint, which is free and does not generate a response.

What is the difference between Claude Sonnet and Opus?

Opus is Anthropic's most capable (and most expensive) model tier, best for complex reasoning and analysis. Sonnet balances capability and cost. Haiku is the fastest and cheapest, ideal for simple tasks. Claude 4.5 Sonnet ($3/1M input) vs Claude 4 Opus ($15/1M input) shows a 5x price difference.

Token Counters by Provider