Question 1

How much can prompt optimization reduce AI API costs?

Accepted Answer

Well-engineered prompts can reduce input token count by 40-70% without quality loss. On GPT-4o at $2.50/M input tokens: cutting 2,000 tokens per request across 100K monthly requests saves $500/month. Combined with caching (50% discount via Anthropic/OpenAI prompt caching) and model routing (cheap model for simple tasks), total cost reduction of 60-80% is achievable.

Question 2

What is prompt caching and how much does it save?

Accepted Answer

Prompt caching stores repeated system prompt tokens and charges a reduced rate on cache hits. OpenAI: 50% discount on cached prompt tokens. Anthropic: up to 90% discount on cached tokens. Requirements: identical prefix tokens across requests. For a 2,000-token system prompt across 100K requests: uncached $500/month → cached $250/month (OpenAI) or $50/month (Anthropic). Best for: chatbots with static system prompts, RAG with shared context.

Question 3

How do I write more token-efficient prompts?

Accepted Answer

Token reduction techniques: (1) Remove filler phrases ('Please', 'Could you', 'I would like you to') — save 5-15 tokens; (2) Use structured formats (JSON, numbered lists) instead of prose instructions; (3) Compress examples — 1 good example beats 5 mediocre ones; (4) Separate static context (cache it) from dynamic context; (5) Use abbreviations in system prompts; (6) Remove repetitive instructions the model already follows by default. Measure token count with tiktoken before/after.

Question 4

When should I switch to a cheaper model?

Accepted Answer

Route to cheaper models when: (1) Task is classification, extraction, or simple transformation (GPT-4o Mini handles 80% of these as well as GPT-4o at 1/25th the cost); (2) Speed matters more than nuance (Haiku/Mini 3-5x faster); (3) Output is short (<500 tokens) and format-predictable. Keep expensive models for: multi-step reasoning, code generation, creative writing, tasks with subtle instructions. A/B test quality at 1% traffic before committing to downgrade.

AI Prompt Cost Optimizer — Reduce API Costs with Better Prompting

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