diff --git a/pyproject.toml b/pyproject.toml
index 624ade170..e1b19e3c9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,7 +26,7 @@ classifiers = [
 ]
 dependencies = [
     "anyio>=4.9",
-    "httpx>=0.27.1",
+    "httpx>=0.27.1,<1.0.0",
     "httpx-sse>=0.4",
     "pydantic>=2.12.0",
     "starlette>=0.48.0; python_version >= '3.14'",
diff --git a/uv.lock b/uv.lock
index 4af3532ea..8f9a5396a 100644
--- a/uv.lock
+++ b/uv.lock
@@ -850,7 +850,7 @@ docs = [
 [package.metadata]
 requires-dist = [
     { name = "anyio", specifier = ">=4.9" },
-    { name = "httpx", specifier = ">=0.27.1" },
+    { name = "httpx", specifier = ">=0.27.1,<1.0.0" },
     { name = "httpx-sse", specifier = ">=0.4" },
     { name = "jsonschema", specifier = ">=4.20.0" },
     { name = "pydantic", specifier = ">=2.12.0" },