Function countTokensViaAnthropic

web/src/app/api/v1/token-count/_post.ts:293–361

(params: {
  messages: TokenCountRequest['messages']
  system: string | undefined
  model: string | undefined
  tools: TokenCountRequest['tools']
  fetch: typeof globalThis.fetch
  logger: Logger
})

}

async function countTokensViaAnthropic(params: {
  messages: TokenCountRequest['messages']
  system: string | undefined
  model: string | undefined
  tools: TokenCountRequest['tools']
  fetch: typeof globalThis.fetch
  logger: Logger
}): Promise<number> {
  const { messages, system, model, tools, fetch, logger } = params

  // Convert messages to Anthropic format
  const anthropicMessages = convertToAnthropicMessages(messages)

  // Convert model from OpenRouter format (e.g. "anthropic/claude-opus-4.5") to Anthropic format (e.g. "claude-opus-4-5-20251101")
  // For non-Anthropic models, use the default Anthropic model for token counting
  const isNonAnthropicModel = !model || !isClaudeModel(model)
  const anthropicModelId = isNonAnthropicModel
    ? DEFAULT_ANTHROPIC_MODEL
    : toAnthropicModelId(model)

  // Use the count_tokens endpoint (beta) or make a minimal request
  const response = await fetch(
    'https://api.anthropic.com/v1/messages/count_tokens',
    {
      method: 'POST',
      headers: {
        'x-api-key': env.ANTHROPIC_API_KEY,
        'anthropic-version': '2023-06-01',
        'anthropic-beta': 'token-counting-2024-11-01',
        'content-type': 'application/json',
      },
      body: JSON.stringify({
        model: anthropicModelId,
        messages: anthropicMessages,
        ...(system && { system }),
        ...(tools && { tools }),
      }),
    },
  )

  if (!response.ok) {
    const errorText = await response.text()
    logger.error(
      {
        status: response.status,
        errorText,
        messages: anthropicMessages,
        system,
        model,
      },
      'Anthropic token count API error',
    )
    throw new Error(`Anthropic API error: ${response.status} - ${errorText}`)
  }

  const data = await response.json()
  const baseTokens = data.input_tokens