1. Enable prompt caching — 50-90% off repeated context
If your prompts have any stable prefix — system messages, retrieved documents, tool definitions, few-shot examples — prompt caching is the single highest-leverage cost cut available in 2026. OpenAI charges cached input at 10% of standard rate (90% off). Anthropic Claude charges cache reads at 10% of standard rate (90% off) and cache writes at 125% of standard rate (a 25% premium that pays for itself if you re-read the cache more than 2 times).
Caching is free to enable on both OpenAI and Anthropic — you just structure your messages so the stable content comes first. The cache hit window is 5-10 minutes on OpenAI (auto-invalidates) and up to 1 hour with Anthropic's extended cache. For agentic workflows that re-call the model 5-50 times in a session, this often cuts the bill 70-85% on its own.
Worked example: an agent loop with 8k tokens of stable system + tools + retrieved context, calling 20 times per session at gpt-5.4. Without caching: 20 × 8k × $2.50/1M = $0.40 per session. With caching (1 write + 19 reads at $0.25/1M cache rate): $0.02 + 19 × 8k × $0.25/1M = $0.04 per session. **90% reduction.**