Alright, let’s talk tokens! 🪙
System prompts, big chunks of context… ching, ching, ching goes your API bill! 💸 Annoying, right?!
Well, Google’s Gemini API is trying to ease that pain, and they’ve got a couple of ways to cache that repetitive stuff. The NEW hotness is… Implicit Caching! This bad boy is ON BY DEFAULT for Gemini 2.5 models!
So, if parts of your request look familiar (think: same system prompt at the start), Gemini tries to be smart and AUTOMATICALLY passes back cost savings if it scores a cache hit! Less work for you, potential savings for your wallet!
So, How Does This “Implicit Magic” Actually Work? 🪄
It sounds almost too good to be true, right? Automatic savings? Well, it’s pretty clever. When you send a request to a Gemini 2.5 model, the system now has a keen eye. If the very beginning of your prompt – what tech folks call the “prefix” – looks familiar, like it matches a prefix you’ve sent in a previous request… 🎯 CACHE HIT!
When this happens, Google says they will “dynamically pass cost savings back to you.” And we’re not talking pennies here. They’re aiming to give you that same awesome 75% token discount on the cached part of your prompt! 🥳 So, if your system prompt is a hefty chunk of tokens, and it gets cached, you’re only paying full price for the new bits you add on, while the cached intro gets that sweet, sweet discount. It’s like the API has a photographic memory for the boring stuff, so you don’t have to pay full price for it every single time.
PRO TIP (Google Recommended! 💡)
Now, to make the most of this awesome new feature, Google has a golden piece of advice – a best practice, if you will. Structure your prompts strategically! Think about it: you want to put all that repetitive, unchanging stuff right at the VERY BEGINNING of your prompt. This includes your system prompts, general instructions, or any large chunks of context that stay the same across multiple calls. Then, you tack on the new, unique stuff – like the user’s specific question, or details that change with each request – at the END. Why? Because the implicit caching looks at that prefix. The longer and more consistent your prefix, the higher the chance of a cache hit and those lovely savings. (If you want to get super nerdy and dive into the nitty-gritty details, the Gemini API docs have got you covered!)
Show Me The Discount!
Naturally, you’ll want to see this magic in action and confirm those savings are rolling in. If you’re using the shiny new Gemini 2.5 models, keep an eye out for a little something called cached_content_token_count in your usage metadata. That number is your golden ticket – it tells you exactly how many of your input tokens benefited from the cache discount. Seeing that number pop up is bound to bring a smile to your face! Sweet
So, you want to become a master of cache-friendly prompts and really dig into the best practices? Google’s got your back. BEST PRACTICES? 👉 Read here!
