Cost optimization patterns for LLM API usage — model routing by task complexity, budget tracking, retry logic, and prompt caching. Use when LLM spend needs to come down, or when routing tasks across model tiers and budgets.

Cost Aware LLM Pipeline Patterns for controlling LLM API costs while maintaining quality. Combines model routing, budget tracking, retry logic, and prompt caching into a composable pipeline. When to Activate Building applications that call LLM APIs (Claude, GPT, etc.) Processing batches of items with varying complexity Need to stay within a budget for API spend Optimizing cost without sacrificing quality on complex tasks Core Concepts 1. Model Routing by Task Complexity Automatically select cheaper models for simple tasks, reserving expensive models for complex ones. 2. Immutable Cost Tracking Track cumulative spend with frozen dataclasses. Each API call returns a new tracker — never mutates state. 3. Narrow Retry Logic Retry only on transient errors. Fail fast on authentication or bad request errors. 4. Prompt Caching Cache long system prompts to avoid resending them on every request. Composition Combine all four techniques in a single pipeline function: Pricing Reference (2026) Model Input ($/1M tokens) Output ($/1M tokens) Relative Cost Haiku 3.5 (legacy) $0.80 $4.00 0.8x Haiku 4.5 $1.00 $5.00 1x Sonnet 5 $2.00 $10.00 2x Sonnet 4.6 $3.00 $15.00 3x Opus 4.8 $5.00 $25.00 5x Fable 5 / Mythos 5 $10.00 $50.00 10x Opus 4.0 / 4.1 (legacy) $15.00 $75.00 15x Best Practices Start with the cheapest model and only route to expensive models when complexity thresholds are met Set explicit budget limits before processing batches — fail early rather than overspend Log model selection decisions so you can tune thresholds based on real data Use prompt caching for system prompts over 1024 tokens — saves both cost and latency Never retry on authentication or validation errors — only transient failures (network, rate limit, server error) Anti Patterns to Avoid Using the most expensive model for all requests regardless of complexity Retrying on all errors (wastes budget on permanent failures) Mutating cost tracking state (makes debugging and auditing difficult) Hardcoding model names throughout the codebase (use constants or config) Ignoring prompt caching for repetitive system prompts When to Use Any application calling Claude, OpenAI, or similar LLM APIs Batch processing pipelines where cost adds up quickly Multi model architectures that need intelligent routing Production systems that need budget guardrails

cost-aware-llm-pipeline