How to recompute your own bill

import re
import unicodedata

_WORD_RE = re.compile(r"\w+|[^\w\s]", re.UNICODE)


def estimate_tokens(text: object) -> int:
    """Deterministic token estimate used for budgeting without model deps."""
    if text is None:
        return 0
    raw = str(text)
    if not raw:
        return 0
    # Word/punctuation estimate plus a char fallback for long compact strings.
    lexical = len(_WORD_RE.findall(raw))
    char_based = max(1, len(raw) // 4)
    return max(lexical, char_based)


def nfc(text: object) -> str:
    return unicodedata.normalize("NFC", "" if text is None else str(text))


def input_tokens(request: dict) -> int:
    """The metered quantity, from the request body alone."""
    task = request.get("task", {})
    total = estimate_tokens(nfc(task.get("prompt")))
    for prompt in task.get("recent_prompts", []):
        total += estimate_tokens(nfc(prompt))
    for record in request.get("records", []):
        total += estimate_tokens(nfc(record.get("text")))
        total += estimate_tokens(nfc(record.get("title")))
    return total

const WORD = "\\p{L}\\p{N}_";
// Python's `\s` also covers U+001C–U+001F and U+0085; JavaScript's does not.
const SPACE = "\\s\\u001C-\\u001F\\u0085";
// U+FEFF is whitespace to JavaScript and not to Python, so it must still be
// counted. It leads the alternation so the negated class cannot swallow it.
const TOKEN_RE = new RegExp(`[${WORD}]+|\\uFEFF|[^${WORD}${SPACE}]`, "gu");

export function estimateTokens(text: unknown): number {
  if (text === null || text === undefined) return 0;
  const raw = String(text);
  if (raw === "") return 0;
  const lexical = (raw.match(TOKEN_RE) ?? []).length;
  // Code points, NOT `.length` — see "Count over Unicode scalar values".
  const charBased = Math.max(1, Math.floor([...raw].length / 4));
  return Math.max(lexical, charBased);
}

const nfc = (text: unknown): string =>
  text === null || text === undefined ? "" : String(text).normalize("NFC");

export function inputTokens(request: {
  records?: { text?: string; title?: string }[];
  task?: { prompt?: string; recent_prompts?: string[] };
}): number {
  const task = request.task ?? {};
  let total = estimateTokens(nfc(task.prompt));
  for (const prompt of task.recent_prompts ?? []) total += estimateTokens(nfc(prompt));
  for (const record of request.records ?? []) {
    total += estimateTokens(nfc(record.text));
    total += estimateTokens(nfc(record.title));
  }
  return total;
}