Cost Aware Llm Pipeline

MODEL_SONNET = "claude-sonnet-5"MODEL_HAIKU = "claude-haiku-4-5-20251001"
_SONNET_TEXT_THRESHOLD = 10_000  # chars_SONNET_ITEM_THRESHOLD = 30     # items
def select_model(    text_length: int,    item_count: int,    force_model: str | None = None,) -> str:    """Select model based on task complexity."""    if force_model is not None:        return force_model    if text_length >= _SONNET_TEXT_THRESHOLD or item_count >= _SONNET_ITEM_THRESHOLD:        return MODEL_SONNET  # Complex task    return MODEL_HAIKU  # Simple task (3-4x cheaper)

from dataclasses import dataclass
@dataclass(frozen=True, slots=True)class CostRecord:    model: str    input_tokens: int    output_tokens: int    cost_usd: float
@dataclass(frozen=True, slots=True)class CostTracker:    budget_limit: float = 1.00    records: tuple[CostRecord, ...] = ()
    def add(self, record: CostRecord) -> "CostTracker":        """Return new tracker with added record (never mutates self)."""        return CostTracker(            budget_limit=self.budget_limit,            records=(*self.records, record),        )
    @property    def total_cost(self) -> float:        return sum(r.cost_usd for r in self.records)
    @property    def over_budget(self) -> bool:        return self.total_cost > self.budget_limit

from anthropic import (    APIConnectionError,    InternalServerError,    RateLimitError,)
_RETRYABLE_ERRORS = (APIConnectionError, RateLimitError, InternalServerError)_MAX_RETRIES = 3
def call_with_retry(func, *, max_retries: int = _MAX_RETRIES):    """Retry only on transient errors, fail fast on others."""    for attempt in range(max_retries):        try:            return func()        except _RETRYABLE_ERRORS:            if attempt == max_retries - 1:                raise            time.sleep(2 ** attempt)  # Exponential backoff    # AuthenticationError, BadRequestError etc. → raise immediately

messages = [    {        "role": "user",        "content": [            {                "type": "text",                "text": system_prompt,                "cache_control": {"type": "ephemeral"},  # Cache this            },            {                "type": "text",                "text": user_input,  # Variable part            },        ],    }]

def process(text: str, config: Config, tracker: CostTracker) -> tuple[Result, CostTracker]:    # 1. Route model    model = select_model(len(text), estimated_items, config.force_model)
    # 2. Check budget    if tracker.over_budget:        raise BudgetExceededError(tracker.total_cost, tracker.budget_limit)
    # 3. Call with retry + caching    response = call_with_retry(lambda: client.messages.create(        model=model,        messages=build_cached_messages(system_prompt, text),    ))
    # 4. Track cost (immutable)    record = CostRecord(model=model, input_tokens=..., output_tokens=..., cost_usd=...)    tracker = tracker.add(record)
    return parse_result(response), tracker