Function countTokensViaOpenAI

web/src/app/api/v1/token-count/_post.ts:128–170

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

const NON_ANTHROPIC_TOKEN_BUFFER = 0.3

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

  const openaiModelId = model.startsWith('openai/')
    ? model.slice('openai/'.length)
    : model

  const input = convertToResponsesApiInput(messages)

  const response = await fetch(
    'https://api.openai.com/v1/responses/input_tokens',
    {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${env.OPENAI_API_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        model: openaiModelId,
        input,
        ...(system && { instructions: system }),
      }),
    },
  )

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

  const data = await response.json()
  return data.input_tokens
}

export type ResponsesApiContentPart =
  | { type: 'input_text'; text: string }