diff --git a/changelog.d/anthropic-sdk-1-human-prompt.fixed.md b/changelog.d/anthropic-sdk-1-human-prompt.fixed.md
new file mode 100644
index 000000000..1e9499caa
--- /dev/null
+++ b/changelog.d/anthropic-sdk-1-human-prompt.fixed.md
@@ -0,0 +1 @@
+Pin the anthropic SDK below 1.0: anthropic 1.0 (released 2026-08-20) removed HUMAN_PROMPT and the temperature keyword the AI analysis services pass to messages.stream(), and both the PR Test job and the Cloud Run image install with unpinned pip, so fresh builds would have failed at import (tests) or on AI-analysis cache misses (production). A contract test now checks the installed SDK's real stream() signature.
diff --git a/pyproject.toml b/pyproject.toml
index 412957b5b..fb5eeb293 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,7 +23,7 @@ classifiers = [
 dependencies = [
     "a2wsgi>=1.10,<2",
     "alembic>=1.14,<2",
-    "anthropic",
+    "anthropic>=0.97.0,<1",
     "assertpy",
     "click>=8,<9",
     "cloud-sql-python-connector",
diff --git a/tests/unit/services/test_anthropic_sdk_contract.py b/tests/unit/services/test_anthropic_sdk_contract.py
new file mode 100644
index 000000000..70eec83c0
--- /dev/null
+++ b/tests/unit/services/test_anthropic_sdk_contract.py
@@ -0,0 +1,30 @@
+"""Guard the installed anthropic SDK against the call shape the services use.
+
+The AI analysis services call ``claude_client.messages.stream(...)`` with a
+``temperature`` keyword. The unit suites mock the client with permissive
+fakes, so an SDK whose real signature dropped that keyword (anthropic 1.x
+removed ``temperature``/``top_p``/``top_k`` and ``HUMAN_PROMPT``) still
+passes every mocked test while failing at runtime on a cache miss. This test
+checks the real installed SDK instead.
+"""
+
+import inspect
+
+import anthropic
+from anthropic.resources.messages import Messages
+
+
+def test_installed_anthropic_sdk_accepts_stream_temperature():
+    parameters = inspect.signature(Messages.stream).parameters
+    assert "temperature" in parameters, (
+        f"anthropic {anthropic.__version__} no longer accepts temperature in "
+        "Messages.stream(); migrate ai_analysis_service before raising the pin"
+    )
+
+
+def test_installed_anthropic_sdk_is_pre_1_0():
+    major = int(anthropic.__version__.split(".")[0])
+    assert major < 1, (
+        f"anthropic {anthropic.__version__} installed; pyproject pins <1 until "
+        "the services are migrated to the 1.x call surface"
+    )
diff --git a/uv.lock b/uv.lock
index d9d78904b..e9dacf541 100644
--- a/uv.lock
+++ b/uv.lock
@@ -2487,7 +2487,7 @@ name = "pexpect"
 version = "4.9.0"
 source = { registry = "https://pypi.org/simple" }
 dependencies = [
-    { name = "ptyprocess" },
+    { name = "ptyprocess", marker = "sys_platform != 'emscripten' and sys_platform != 'win32'" },
 ]
 sdist = { url = "https://files.pythonhosted.org/packages/42/92/cc564bf6381ff43ce1f4d06852fc19a2f11d180f23dc32d9588bee2f149d/pexpect-4.9.0.tar.gz", hash = "sha256:ee7d41123f3c9911050ea2c2dac107568dc43b2d3b0c7557a33212c398ead30f", size = 166450, upload-time = "2023-11-25T09:07:26.339Z" }
 wheels = [
@@ -2642,7 +2642,7 @@ models = [
 
 [[package]]
 name = "policyengine-api"
-version = "3.48.2"
+version = "3.49.1"
 source = { editable = "." }
 dependencies = [
     { name = "a2wsgi" },
@@ -2695,7 +2695,7 @@ dev = [
 requires-dist = [
     { name = "a2wsgi", specifier = ">=1.10,<2" },
     { name = "alembic", specifier = ">=1.14,<2" },
-    { name = "anthropic" },
+    { name = "anthropic", specifier = ">=0.97.0,<1" },
     { name = "assertpy" },
     { name = "build", marker = "extra == 'dev'" },
     { name = "click", specifier = ">=8,<9" },