AI Architecture Patterns.

Pattern 1: The Gateway

The Gateway pattern is your front door. Every request enters through a single point that handles authentication, rate limiting, input validation, and request normalization before anything touches a model. ```python class AIGateway: def __init__(self, rate_limiter, validator, auth): self.rate_limiter = rate_limiter self.validator = validator self.auth = auth async def handle(self, request): # Step 1: Authenticate user = self.auth.verify(request.token) # Step 2: Rate limit per user tier if not self.rate_limiter.allow(user.tier, user.id): raise RateLimitError(retry_after=self.rate_limiter.retry_after(user.id)) # Step 3: Validate and sanitize input clean_input = self.validator.sanitize(request.body) if len(clean_input.tokens) > user.tier.max_tokens: raise TokenLimitError(max=user.tier.max_tokens) # Step 4: Forward to processing layer return await self.processor.process(clean_input, user) ``` The Gateway never makes AI decisions. It protects the system, normalizes inputs, and enforces contracts. Think of it as the bouncer -- it decides who gets in, not what happens inside.

Pattern 2: The Router

The Router pattern directs requests to the right handler based on intent, complexity, or content type. This is where you stop paying GPT-4 prices for GPT-3.5 work. ```python class ModelRouter: ROUTES = { "simple_faq": {"model": "gpt-4o-mini", "max_tokens": 200}, "technical": {"model": "claude-sonnet-4-20250514", "max_tokens": 2000}, "complex": {"model": "claude-opus-4-20250514", "max_tokens": 4000}, "code_gen": {"model": "claude-sonnet-4-20250514", "max_tokens": 8000}, } async def route(self, request): # Classify with a fast, cheap model intent = await self.classifier.classify(request.text) # Select configuration config = self.ROUTES.get(intent, self.ROUTES["complex"]) # Check cache before calling model cached = await self.cache.get(request.text, intent) if cached: return cached return await self.call_model(request, config) ``` The classifier itself is typically a fine-tuned small model or even a rules-based system. You do not need AI to decide which AI to use -- a regex or keyword match handles 70% of routing decisions.