import anthropic

client = anthropic.Anthropic()   # reads ANTHROPIC_API_KEY from the environment

# Must clear the model's minimum cacheable length or nothing is cached at all.
LONG_INSTRUCTIONS = "You are a precise technical editor. " * 400

def ask(question: str):
    return client.messages.create(
        model="claude-sonnet-4-6",
        max_tokens=512,
        system=[
            {
                "type": "text",
                "text": LONG_INSTRUCTIONS,
                "cache_control": {"type": "ephemeral"},   # everything above is cacheable
            }
        ],
        messages=[{"role": "user", "content": question}],
    )

for question in ["Summarize section 3.", "Now rewrite it for a beginner."]:
    resp = ask(question)
    u = resp.usage
    print(
        f"write={u.cache_creation_input_tokens} "
        f"read={u.cache_read_input_tokens} "
        f"uncached={u.input_tokens}"
    )

# Output:
"write=2823  read=0     uncached=14"
"write=0     read=2823  uncached=17"