【MCP互換性ガイド】2026-07-28 リリース候補の変更点と移行手順：ステートレス化・認証強化・拡張機能フレームワーク

import httpx

# 初期化ハンドシェイク
session_id = None
async with httpx.AsyncClient() as client:
    # Step 1: initialize
    resp = await client.post("https://mcp-server.example.com/mcp", json={
        "jsonrpc": "2.0",
        "id": 1,
        "method": "initialize",
        "params": {
            "protocolVersion": "2025-11-25",
            "capabilities": {}
        }
    })
    data = resp.json()
    session_id = data["result"]["sessionId"]

    # Step 2: initialized notification
    await client.post("https://mcp-server.example.com/mcp", json={
        "jsonrpc": "2.0",
        "method": "notifications/initialized"
    })

    # Step 3: 以降は session_id をヘッダーに含めてリクエスト
    resp = await client.post(
        "https://mcp-server.example.com/mcp",
        headers={"Mcp-Session-Id": session_id},
        json={
            "jsonrpc": "2.0",
            "id": 2,
            "method": "tools/list"
        }
    )

import httpx

# ハンドシェイク不要。毎リクエスト自己完結
async with httpx.AsyncClient() as client:
    resp = await client.post(
        "https://mcp-server.example.com/mcp",
        headers={
            "MCP-Protocol-Version": "2026-07-28",
            "Mcp-Method": "tools/list",
        },
        json={
            "jsonrpc": "2.0",
            "id": 1,
            "method": "tools/list",
            "params": {
                "_meta": {
                    "protocolVersion": "2026-07-28",
                    "capabilities": {}
                }
            }
        }
    )

# FastMCP (OpenMCP) での移行例
from mcp import FastMCP

# サーバー側: プロトコルバージョン指定
mcp = FastMCP(
    "My MCP Server",
    protocol_version="2026-07-28"  # 指定しない場合も自動検出
)

@mcp.tool()
def get_weather(city: str) -> str:
    """都市の天気を取得"""
    return f"{city}の天気は晴れです"

# 2026-07-28: Tasks 拡張を使った長時間処理の例
import httpx

async with httpx.AsyncClient() as client:
    # ツール呼び出し → タスク生成
    resp = await client.post(
        "https://mcp-server.example.com/mcp",
        headers={
            "MCP-Protocol-Version": "2026-07-28",
            "Mcp-Method": "tools/call",
        },
        json={
            "jsonrpc": "2.0",
            "id": 1,
            "method": "tools/call",
            "params": {
                "name": "long_running_analysis",
                "arguments": {"dataset": "sales_2026"},
                "_meta": {"protocolVersion": "2026-07-28"}
            }
        }
    )
    data = resp.json()
    task_handle = data["result"]["taskHandle"]

    # タスク進捗確認
    status = await client.post(
        "https://mcp-server.example.com/mcp",
        headers={
            "MCP-Protocol-Version": "2026-07-28",
            "Mcp-Method": "tasks/get",
        },
        json={
            "jsonrpc": "2.0",
            "id": 2,
            "method": "tasks/get",
            "params": {"handle": task_handle}
        }
    )

# デュアルスタック MCP サーバーの例
from mcp import FastMCP
from mcp.transport import SSE, StreamableHTTP

mcp = FastMCP("My Server", protocol_version="2026-07-28")

# 両方のトランスポートを同時に提供
mcp.mount_transport(SSE(port=8000))         # 後方互換性用
mcp.mount_transport(StreamableHTTP(port=8001))  # 新プロトコル

@mcp.tool()
def search_docs(query: str) -> str:
    return f"Searching for: {query}"

# クライアント側の接続確認
curl -s -X POST https://mcp-server.example.com:8001/mcp \
  -H "MCP-Protocol-Version: 2026-07-28" \
  -H "Mcp-Method: tools/list" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{"_meta":{"protocolVersion":"2026-07-28"}}}'

# OAuth 2.1 認証フローの例（Client ID Metadata Documents）
curl -s https://mcp-auth.example.com/.well-known/oauth-authorization-server \
  -H "Accept: application/json"

# 応答例:
# {
#   "issuer": "https://mcp-auth.example.com",
#   "authorization_endpoint": "https://mcp-auth.example.com/authorize",
#   "token_endpoint": "https://mcp-auth.example.com/token",
#   "client_id_metadata_docs_supported": true
# }

# JSON Schema 2020-12 の新しい表現力
@mcp.tool()
def analyze_data(
    dataset: str,
    filters: dict | None = None,
    aggregation: str = "sum"
) -> str:
    """
    データ分析ツール
    JSON Schema 2020-12 により、複合型の条件付きバリデーションが可能に
    """
    pass