Anthropic Reference Architecture

Overview

Three validated architecture patterns for Claude API integrations: synchronous API gateway, async queue-based processing, and multi-model routing.

Architecture 1: Sync API Gateway (Simple)

User → API Gateway → Claude Service → Messages API
                                     ↓
                                   Response → User

# Best for: chatbots, interactive tools, low-volume (<100 RPM)
from fastapi import FastAPI
import anthropic

app = FastAPI()
client = anthropic.Anthropic(max_retries=3, timeout=60.0)

@app.post("/chat")
async def chat(prompt: str):
    msg = client.messages.create(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        messages=[{"role": "user", "content": prompt}]
    )
    return {"text": msg.content[0].text, "tokens": msg.usage.output_tokens}

Architecture 2: Async Queue-Based (Scalable)

User → API → Queue (Redis/SQS) → Worker Pool → Messages API
  ↑                                                ↓
  └──────────── Status/Result ←── Result Store ←───┘

# Best for: batch processing, high-volume, background tasks
from redis import Redis
from rq import Queue
import anthropic

redis = Redis()
task_queue = Queue("claude-tasks", connection=redis)
result_store = Redis(db=1)

def process_task(task_id: str, prompt: str, model: str):
    client = anthropic.Anthropic()
    msg = client.messages.create(
        model=model,
        max_tokens=1024,
        messages=[{"role": "user", "content": prompt}]
    )
    result_store.setex(f"result:{task_id}", 3600, msg.content[0].text)

# Enqueue
import uuid
task_id = str(uuid.uuid4())
task_queue.enqueue(process_task, task_id, prompt, "claude-sonnet-4-20250514")

Architecture 3: Multi-Model Router

User → Router → Haiku    (classify/extract)
              → Sonnet   (general/code)
              → Opus     (research/complex)
              → Batches  (bulk/offline)

class ModelRouter:
    def __init__(self):
        self.client = anthropic.Anthropic()
        self.classifier = anthropic.Anthropic()  # Can be same client

    def route_and_execute(self, prompt: str, context: dict) -> str:
        # Step 1: Classify with Haiku (cheap, fast)
        classification = self.classifier.messages.create(
            model="claude-haiku-4-20250514",
            max_tokens=32,
            messages=[{
                "role": "user",
                "content": f"Classify this request as: simple|moderate|complex|bulk\n\n{prompt[:200]}"
            }]
        )
        complexity = classification.content[0].text.strip().lower()

        # Step 2: Route to appropriate model
        model_map = {
            "simple": "claude-haiku-4-20250514",
            "moderate": "claude-sonnet-4-20250514",
            "complex": "claude-opus-4-20250514",
        }
        model = model_map.get(complexity, "claude-sonnet-4-20250514")

        # Step 3: Execute with selected model
        msg = self.client.messages.create(
            model=model,
            max_tokens=4096,
            messages=[{"role": "user", "content": prompt}]
        )
        return msg.content[0].text

Project Layout

my-claude-app/
├── src/
│   ├── main.py              # FastAPI app
│   ├── claude/
│   │   ├── client.py         # Singleton + config
│   │   ├── router.py         # Model routing logic
│   │   ├── tools.py          # Tool definitions
│   │   └── prompts/          # System prompts as files
│   ├── workers/
│   │   └── claude_worker.py  # Queue consumer
│   └── middleware/
│       ├── rate_limiter.py   # App-level rate limiting
│       └── cost_tracker.py   # Spend monitoring
├── tests/
│   ├── unit/                 # Mocked tests
│   └── integration/          # Live API tests
└── config/
    ├── .env.development
    ├── .env.staging
    └── .env.production

Error Handling

Architecture	Failure Mode	Mitigation
Sync Gateway	429/5xx blocks user	Circuit breaker + fallback response
Queue-Based	Worker crashes	Dead-letter queue + retry policy
Multi-Model	Router misclassifies	Default to Sonnet (safest middle)

Prerequisites

Choose the workload class, availability/latency SLOs, data classification, approved destinations, and synchronous versus asynchronous behavior with an owner.
Provide an isolated workspace, least-privileged secret-manager credential, synthetic fixtures, bounded queue/concurrency settings, and a tested rollback/circuit-breaker plan.
Define idempotency, retention, dead-letter, and redacted evidence requirements before selecting an architecture.

Instructions

Select the smallest architecture that meets the workload: gateway for interactive calls, queue for asynchronous work, or a router only when model policy and quality tests justify it.
Keep credentials and policy enforcement at the service boundary. Validate model, token, rate, data-class, source, and destination scope before enqueueing or sending a request.
Exercise success, timeout, 429/5xx, duplicate, queue-retry, tool-use, and partial-response paths with synthetic fixtures. Ensure traces and result stores exclude prompts, responses, and secrets.
Canary the selected topology in an isolated workspace, observe SLOs/cost/rate limits, and require approval before production traffic. Preserve the prior topology and configuration.
On policy, reliability, or cost regression, open the circuit or pause workers, drain/quarantine unsafe work, roll back, and retain a redacted architecture receipt.

Output

Produce an architecture receipt naming the selected pattern, component/config digests, workspace and model classes, scope/idempotency/retention controls, synthetic test results, canary and SLO outcomes, approval, and rollback reference. Exclude request content, user identifiers, credentials, and raw queue payloads.

Examples

For 100 synthetic asynchronous classification jobs, use a sandbox queue with a bounded worker pool, assert duplicate_jobs=0; contacts_exported=0; content_logged=0, and canary one internal consumer. A queue failure yields paused=true; dead_letter=synthetic-only; rollback=worker-v1.

Resources

Next Steps

For multi-environment setup, see anth-multi-env-setup.