Split View: LLM API 비용을 90% 줄이는 실전 최적화 전략

Scenario: B2B SaaS, 5,000 daily active users

Usage pattern:
- 1 user × 10 conversations per day
- 1 conversation = 200 input tokens + 300 output tokens

Daily token usage:
5,000 users × 10 conversations × 500 tokens = 25,000,000 tokens/day

Monthly:
25,000,000 × 30 = 750,000,000 tokens/month

Monthly cost comparison:
GPT-4o ($2.50/1M input + $10/1M output):
  → Input $37,500 + Output $45,000 = $82,500/month

GPT-4o-mini ($0.15/1M input + $0.60/1M output):
  → Input $2,250 + Output $2,700 = $4,950/month

Self-hosted Llama: ~$500-2,000/month

import anthropic

client = anthropic.Anthropic()

# A long system prompt that gets sent with every single request
COMPANY_KNOWLEDGE_BASE = """
[Thousands of tokens of company documentation, product info, policies...]
...sending this on every request without caching is burning money.
"""

def chat_with_caching(user_message: str) -> dict:
    response = client.messages.create(
        model="claude-3-5-sonnet-20241022",
        max_tokens=1024,
        system=[
            {
                "type": "text",
                "text": COMPANY_KNOWLEDGE_BASE,
                "cache_control": {"type": "ephemeral"}  # Cache this block!
            },
            {
                "type": "text",
                "text": "You are a customer support specialist. Answer based on the company info above."
                # Not cached: short, may change
            }
        ],
        messages=[{"role": "user", "content": user_message}]
    )

    usage = response.usage
    print(f"Cache write tokens: {usage.cache_creation_input_tokens} (1.25x cost)")
    print(f"Cache read tokens:  {usage.cache_read_input_tokens} (0.1x cost — 90% off!)")
    print(f"Normal input tokens: {usage.input_tokens} (1x cost)")

    return {
        "content": response.content[0].text,
        "cache_hit": usage.cache_read_input_tokens > 0
    }

# First call: cache creation (costs 1.25x, written to cache)
result1 = chat_with_caching("What's your refund policy?")

# All subsequent calls: cache hit (costs 0.1x — 90% savings!)
result2 = chat_with_caching("How long does shipping take?")
result3 = chat_with_caching("What's the warranty period?")

from openai import OpenAI
client = OpenAI()

# OpenAI automatically caches prompts over 1,024 tokens
# 50% discount applied automatically, no configuration needed
response = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {
            "role": "system",
            # Longer than 1,024 tokens → auto-cached at 50% discount
            "content": LONG_SYSTEM_PROMPT   # 2,000+ tokens recommended
        },
        {"role": "user", "content": "user question here"}
    ]
)

# Check if cache was hit
usage = response.usage
if hasattr(usage, 'prompt_tokens_details'):
    cached = usage.prompt_tokens_details.cached_tokens
    total_input = usage.prompt_tokens
    savings_pct = (cached / total_input * 50) if total_input > 0 else 0
    print(f"Cached: {cached}/{total_input} tokens ({savings_pct:.1f}% cost reduction)")

from openai import OpenAI
import re

client = OpenAI()

class ModelRouter:
    """Route requests to the cheapest model that can handle them"""

    SIMPLE_PATTERNS = [
        r"^(what is|what are|define|who is|when was|where is)",
        r"^(translate|how do you say|what does .* mean)",
        r"(yes or no|true or false|is it)",
    ]

    COMPLEX_PATTERNS = [
        r"(analyze|compare|design|architect|evaluate)",
        r"(step.by.step|detailed|comprehensive|in.depth)",
        r"(implement|code|build|create a system|write a program)",
        r"(explain why|what causes|pros and cons|trade.?offs)",
        r"(review|critique|refactor|optimize)",
    ]

    def classify(self, query: str) -> str:
        lower = query.lower()

        if any(re.search(p, lower) for p in self.COMPLEX_PATTERNS):
            return "complex"

        if (len(query.split()) < 20 and
                any(re.search(p, lower) for p in self.SIMPLE_PATTERNS)):
            return "simple"

        if len(query) > 500:
            return "complex"

        return "medium"

    def complete(self, query: str, system: str = "") -> dict:
        complexity = self.classify(query)

        messages = []
        if system:
            messages.append({"role": "system", "content": system})
        messages.append({"role": "user", "content": query})

        if complexity in ("simple", "medium"):
            # GPT-4o-mini: ~60x cheaper than GPT-4o
            response = client.chat.completions.create(
                model="gpt-4o-mini",
                messages=messages,
                max_tokens=500 if complexity == "medium" else 200
            )
            model = "gpt-4o-mini"
        else:
            # Complex reasoning: use capable model
            response = client.chat.completions.create(
                model="gpt-4o",
                messages=messages
            )
            model = "gpt-4o"

        return {
            "answer": response.choices[0].message.content,
            "model": model,
            "complexity": complexity,
            "tokens": response.usage.total_tokens
        }


# Real-world cost impact:
# Assume traffic distribution: 60% simple, 25% medium, 15% complex
# Cost with all GPT-4o:    100% × $12.50/1M avg = $12.50
# Cost with routing:       85% × $0.375 + 15% × $12.50 = $0.32 + $1.88 = $2.20
# → ~82% cost reduction

router = ModelRouter()

examples = [
    "What is a transformer architecture?",     # simple → mini
    "Implement a LRU cache in Python",          # complex → GPT-4o
    "What does HNSW stand for?",                # simple → mini
    "Design a distributed rate limiting system", # complex → GPT-4o
]

for q in examples:
    result = router.complete(q)
    print(f"[{result['complexity'].upper()}] → {result['model']} | {q[:50]}")

import hashlib
import numpy as np
from openai import OpenAI
from datetime import datetime, timedelta

client = OpenAI()

class SemanticCache:
    """
    Cache responses by semantic meaning, not exact text.
    "What is RAG?" and "Explain RAG to me" return the same cached result.
    """

    def __init__(self, similarity_threshold: float = 0.92, ttl_hours: int = 24):
        self.cache: dict = {}
        self.threshold = similarity_threshold
        self.ttl = timedelta(hours=ttl_hours)
        self.stats = {"hits": 0, "misses": 0}

    def _embed(self, text: str) -> list:
        return client.embeddings.create(
            input=text,
            model="text-embedding-3-small",
            dimensions=256   # Small dims for fast cache lookup
        ).data[0].embedding

    def _similarity(self, a: list, b: list) -> float:
        a_np, b_np = np.array(a), np.array(b)
        return float(np.dot(a_np, b_np) / (np.linalg.norm(a_np) * np.linalg.norm(b_np)))

    def lookup(self, query: str) -> tuple:
        """Returns (cached_response, similarity) or (None, 0)"""
        query_emb = self._embed(query)
        best_score, best_response = 0.0, None

        for entry in self.cache.values():
            if datetime.now() - entry["ts"] > self.ttl:
                continue
            score = self._similarity(query_emb, entry["emb"])
            if score > best_score:
                best_score, best_response = score, entry["response"]

        if best_score >= self.threshold:
            self.stats["hits"] += 1
            return best_response, best_score

        self.stats["misses"] += 1
        return None, best_score

    def store(self, query: str, response: str) -> None:
        key = hashlib.md5(query.encode()).hexdigest()
        self.cache[key] = {
            "emb": self._embed(query),
            "response": response,
            "ts": datetime.now()
        }

    def ask(self, query: str, model: str = "gpt-4o-mini") -> dict:
        cached, score = self.lookup(query)

        if cached:
            return {"response": cached, "source": "cache", "similarity": score}

        response = client.chat.completions.create(
            model=model,
            messages=[{"role": "user", "content": query}]
        ).choices[0].message.content

        self.store(query, response)
        return {"response": response, "source": "api", "similarity": 0}

    @property
    def hit_rate(self) -> float:
        total = self.stats["hits"] + self.stats["misses"]
        return self.stats["hits"] / total if total else 0


# Pre-warm cache with FAQ
cache = SemanticCache(similarity_threshold=0.92)
faqs = [
    "What is your refund policy?",
    "How long does shipping take?",
    "How do I reset my password?",
    "What payment methods do you accept?",
]
for q in faqs:
    cache.ask(q)  # Stores in cache

# These semantically similar queries hit cache:
r1 = cache.ask("Can I get a refund?")         # Similar to "refund policy" → cache
r2 = cache.ask("How fast is delivery?")        # Similar to "shipping take" → cache
r3 = cache.ask("I forgot my password")         # Similar to "reset password" → cache

print(f"Cache hit rate: {cache.hit_rate:.1%}")  # ~75% for FAQ-heavy workloads

from openai import OpenAI
import json
import tempfile

client = OpenAI()

def submit_batch_job(texts: list, task_description: str) -> str:
    """
    Process large volumes of text at 50% cost reduction.
    Completed within 24 hours.
    Ideal for: sentiment analysis, classification, summarization, translation
    """

    requests = [
        {
            "custom_id": f"item-{i}",
            "method": "POST",
            "url": "/v1/chat/completions",
            "body": {
                "model": "gpt-4o-mini",
                "messages": [
                    {"role": "system", "content": task_description},
                    {"role": "user", "content": text}
                ],
                "max_tokens": 100,
                "response_format": {"type": "json_object"}
            }
        }
        for i, text in enumerate(texts)
    ]

    # Write JSONL file
    with tempfile.NamedTemporaryFile(mode='w', suffix='.jsonl', delete=False) as f:
        for req in requests:
            f.write(json.dumps(req) + '\n')
        tmp_path = f.name

    # Upload and submit
    with open(tmp_path, 'rb') as f:
        batch_file = client.files.create(file=f, purpose="batch")

    batch = client.batches.create(
        input_file_id=batch_file.id,
        endpoint="/v1/chat/completions",
        completion_window="24h"
    )

    print(f"Batch submitted: {batch.id}")
    print(f"Cost: 50% less than synchronous API")
    print(f"Expected completion: within 24 hours")
    return batch.id


def retrieve_batch_results(batch_id: str) -> list:
    batch = client.batches.retrieve(batch_id)

    if batch.status != "completed":
        print(f"Status: {batch.status} — not ready yet")
        return []

    content = client.files.content(batch.output_file_id)
    results = []
    for line in content.text.strip().split('\n'):
        item = json.loads(line)
        body = item["response"]["body"]
        answer = body["choices"][0]["message"]["content"]
        results.append({
            "id": item["custom_id"],
            "result": json.loads(answer) if answer.startswith('{') else answer
        })

    return results


# Example: Classify 10,000 support tickets overnight
tickets = ["My order hasn't arrived", "I love this product!", "Wrong item received"] * 3334

batch_id = submit_batch_job(
    texts=tickets,
    task_description='Classify the support ticket. Respond in JSON: {"category": "shipping|product|billing|other", "priority": "high|medium|low", "sentiment": "positive|negative|neutral"}'
)

# Run this the next day
results = retrieve_batch_results(batch_id)

from openai import OpenAI
from pydantic import BaseModel
from typing import Literal

client = OpenAI()

# Bad: verbose prose response (wastes tokens)
def analyze_verbose(text: str) -> str:
    response = client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[{"role": "user", "content": f"Analyze the sentiment of: {text}"}]
    )
    # Returns: "The sentiment of this text is overwhelmingly positive. The author expresses..."
    # Typical: 80-200 output tokens
    return response.choices[0].message.content


# Good: structured minimal output
class SentimentResult(BaseModel):
    sentiment: Literal["positive", "negative", "neutral"]
    confidence: float
    reason: str   # Max 5 words enforced by prompt

def analyze_structured(text: str) -> SentimentResult:
    response = client.beta.chat.completions.parse(
        model="gpt-4o-mini",
        messages=[
            {
                "role": "system",
                "content": "Classify sentiment. Reason must be 5 words max."
            },
            {"role": "user", "content": text}
        ],
        response_format=SentimentResult
    )
    # Returns: {"sentiment": "positive", "confidence": 0.94, "reason": "enthusiastic praise"}
    # Typical: 20-30 output tokens → 85% savings
    return response.choices[0].message.parsed


# Token-aware prompting
def summarize_concisely(text: str, target_words: int = 50) -> str:
    response = client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[
            {
                "role": "system",
                "content": f"Summarize in exactly {target_words} words or fewer. Be direct. No preamble."
            },
            {"role": "user", "content": text}
        ],
        max_tokens=target_words * 2  # Hard limit as safety net
    )
    return response.choices[0].message.content


# For JSON tasks, avoid asking the model to "explain" anything
EXTRACTION_PROMPT = """Extract the requested data. Return ONLY valid JSON. No explanation.
If a field is missing, use null."""

def extract_structured_data(document: str, schema: dict) -> dict:
    response = client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[
            {"role": "system", "content": EXTRACTION_PROMPT},
            {"role": "user", "content": f"Schema: {json.dumps(schema)}\n\nDocument: {document}"}
        ],
        response_format={"type": "json_object"}
    )
    return json.loads(response.choices[0].message.content)

from collections import defaultdict
from datetime import date
from openai import OpenAI
import json

client = OpenAI()

class CostTracker:
    """Real-time LLM API cost tracking with budget alerts"""

    # 2025 pricing ($/1M tokens)
    PRICING = {
        "gpt-4o":           {"input": 2.50,  "output": 10.00},
        "gpt-4o-mini":      {"input": 0.15,  "output": 0.60},
        "claude-3-5-sonnet-20241022": {"input": 3.00, "output": 15.00},
        "claude-3-haiku-20240307":    {"input": 0.25, "output": 1.25},
    }

    def __init__(self, daily_budget: float = 100.0):
        self.daily_budget = daily_budget
        self.by_model = defaultdict(lambda: {"in": 0, "out": 0, "cost": 0.0})
        self.by_day = defaultdict(float)

    def record(self, model: str, input_tokens: int, output_tokens: int) -> float:
        p = self.PRICING.get(model, {"input": 0, "output": 0})
        cost = (input_tokens * p["input"] + output_tokens * p["output"]) / 1_000_000
        today = date.today().isoformat()

        self.by_model[model]["in"] += input_tokens
        self.by_model[model]["out"] += output_tokens
        self.by_model[model]["cost"] += cost
        self.by_day[today] += cost

        daily_so_far = self.by_day[today]
        if daily_so_far > self.daily_budget * 0.8:
            print(f"WARNING: 80% of daily budget used (${daily_so_far:.2f} / ${self.daily_budget:.2f})")
        if daily_so_far > self.daily_budget:
            raise RuntimeError(f"Daily budget exceeded! ${daily_so_far:.2f} > ${self.daily_budget:.2f}")

        return cost

    def report(self) -> None:
        total = sum(d["cost"] for d in self.by_model.values())
        today = date.today().isoformat()
        print(f"\n{'='*50}")
        print(f"Today's spend: ${self.by_day[today]:.4f} / ${self.daily_budget:.2f} budget")
        print(f"Total tracked: ${total:.4f}")
        print(f"\nBy model:")
        for model, d in sorted(self.by_model.items(), key=lambda x: -x[1]["cost"]):
            pct = d["cost"] / total * 100 if total else 0
            print(f"  {model:<45} ${d['cost']:.4f} ({pct:.1f}%)")
            print(f"    {d['in']:>12,} input | {d['out']:>12,} output tokens")


tracker = CostTracker(daily_budget=50.0)

def tracked_call(model: str, messages: list, **kwargs) -> str:
    """Drop-in replacement for chat completions with cost tracking"""
    response = client.chat.completions.create(model=model, messages=messages, **kwargs)
    tracker.record(model, response.usage.prompt_tokens, response.usage.completion_tokens)
    return response.choices[0].message.content

Baseline: 100,000 requests/month, GPT-4o, avg 1,000 tokens/request

Before optimization:
100,000 × 1,000 × ($2.50 + $10.00) / 1,000,000 = $1,250/month

After all strategies:
1. Prompt Caching (80% of requests, 85% reduction):   saves ~$850
2. Model routing (70% to mini):                        saves ~$280 additional
3. Semantic caching (40% cache hit rate):              saves ~$48 additional
4. Batch API (20% of requests):                        saves ~$24 additional
5. Output optimization (30% shorter outputs):          saves ~$24 additional

Optimized monthly cost: ~$24/month
Savings: ~98% (in ideal scenario, 60-80% realistic)