agents

The same 2,000 tokens are prefilled a thousand times an hour. Caching their KV by content turns that into one prefill and a table lookup, and a radix tree is what makes multi-turn and branching agents share it too.

Both engines cache prefixes, so the choice is not about whether the feature exists. It is about how much of your traffic shares a prefix, what the cache eviction does under pressure, and which tuning model your team can actually operate.

Tool calling passes through four layers and a break in any one produces the same symptom, so the debugging is a bisection rather than an investigation. Which layer the size of the drop points at, the deploy diff that usually contains the answer, and why no latency metric moved.

An agent thinks for a second, runs a tool for a minute, and repeats a hundred times over an hour. The session state machine and where each piece lives, the sandbox per session with its cold-start budget, the KV cache that should survive the tool call, and checkpoints that resume a step rather than an hour.