diff --git a/pyproject.toml b/pyproject.toml
index 330d0031..37f019ce 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,7 +26,7 @@ dependencies = [
     "openai>=2.37",
     "anthropic>=0.108",  # claude-fable-5 support; hard runtime floor is 0.105 (mid-conversation system blocks)
     "httpx>=0.28",
-    "mcp>=1.27",
+    "mcp>=1.27,<2",  # v2 is a breaking rewrite (2.0.0a1 live 2026-06-11; stable ~2026-07-27) — streamablehttp_client removed, 2-tuple transport, snake_case types; migrate deliberately
     "starlette>=1.0.1",  # PYSEC-2026-161: host-header path-injection in URL reconstruction (auth-bypass on apps comparing reconstructed URL paths)
     "uvicorn>=0.34",
     "sse-starlette>=2.0",
diff --git a/uv.lock b/uv.lock
index 70c1b74b..70c56fa4 100644
--- a/uv.lock
+++ b/uv.lock
@@ -2385,7 +2385,7 @@ requires-dist = [
     { name = "httpx", specifier = ">=0.28" },
     { name = "httpx-sse", specifier = ">=0.4" },
     { name = "lacme", specifier = ">=1.0.5" },
-    { name = "mcp", specifier = ">=1.27" },
+    { name = "mcp", specifier = ">=1.27,<2" },
     { name = "mypy", marker = "extra == 'dev'", specifier = ">=1.14" },
     { name = "openai", specifier = ">=2.37" },
     { name = "psycopg", extras = ["binary"], specifier = ">=3.2" },