Gemini 2.5 Models now support implicit caching- Google Developers Blog

Introduces implicit caching for Gemini 2.5 models, which automatically applies cost savings (75% token discount) for requests sharing a common prefix with previous requests. This is achieved by dynamically passing savings back to developers. Best practices for increasing cache hits include keeping the beginning of the prompt consistent and adding variable content at the end. Minimum request sizes for Gemini 2.5 Flash and Pro have been reduced to 1024 and 2048 tokens, respectively, to improve cache eligibility. Explicit caching remains available for guaranteed cost savings.