Claude Fable 5.1 & Claude Opus 5: 1M Context, Secure Tool Sandbox & Subagent Coordination

import json
import subprocess
from typing import Any
import anthropic

client = anthropic.Anthropic()
ALLOWED: dict[str, list[str]] = {
    "ruff": ["ruff", "check", "."],
    "pytest": ["pytest", "-q", "--disable-warnings", "--maxfail=1"],
    "mypy": ["mypy", "."],
}

def run_check(name: str) -> dict[str, Any]:
    if name not in ALLOWED:
        return {"ok": False, "error": "tool not allowlisted"}
    cp = subprocess.run(
        ALLOWED[name], capture_output=True, text=True, timeout=120, shell=False
    )
    return {
        "ok": cp.returncode == 0,
        "returncode": cp.returncode,
        "stdout": cp.stdout[-12000:],
        "stderr": cp.stderr[-12000:],
    }

tools = [{
    "name": "run_check",
    "description": "Run an allowlisted repository quality check.",
    "input_schema": {
        "type": "object",
        "properties": {"name": {"type": "string", "enum": list(ALLOWED)}},
        "required": ["name"],
        "additionalProperties": False,
    },
    "strict": True,
    "cache_control": {"type": "ephemeral"},
}]

messages: list[dict[str, Any]] = [{
    "role": "user",
    "content": "Inspect the repository quality. Call the smallest useful check, then explain the result.",
}]

while True:
    msg = client.messages.create(
        model="claude-opus-5",
        max_tokens=1800,
        cache_control={"type": "ephemeral"},
        system="You are a senior refactoring verifier. Never claim a check passed unless the tool says so.",
        tools=tools,
        messages=messages,
    )
    messages.append({"role": "assistant", "content": msg.content})
    calls = [b for b in msg.content if b.type == "tool_use"]
    if not calls:
        print("".join(b.text for b in msg.content if b.type == "text"))
        break
    results = []
    for call in calls:
        result = run_check(str(call.input["name"]))
        results.append({
            "type": "tool_result",
            "tool_use_id": call.id,
            "content": json.dumps(result),
            "cache_control": {"type": "ephemeral"},
        })
    messages.append({"role": "user", "content": results})