diff --git a/src/strands/models/anthropic.py b/src/strands/models/anthropic.py
index b5f6fcf91..c602a3926 100644
--- a/src/strands/models/anthropic.py
+++ b/src/strands/models/anthropic.py
@@ -8,6 +8,7 @@
 import logging
 import mimetypes
 from collections.abc import AsyncGenerator
+from importlib.metadata import PackageNotFoundError, version
 from typing import Any, TypedDict, TypeVar, cast
 
 import anthropic
@@ -76,6 +77,19 @@ def __init__(self, *, client_args: dict[str, Any] | None = None, **model_config:
         logger.debug("config=<%s> | initializing", self.config)
 
         client_args = client_args or {}
+
+        # Add User-Agent header if not already set
+        if "default_headers" not in client_args:
+            client_args["default_headers"] = {}
+        else:
+            client_args["default_headers"] = {**client_args["default_headers"]}
+        if "User-Agent" not in client_args["default_headers"]:
+            try:
+                strands_version = version("strands-agents")
+            except PackageNotFoundError:
+                strands_version = "unknown"
+            client_args["default_headers"]["User-Agent"] = f"strands-agents/{strands_version}"
+
         self.client = anthropic.AsyncAnthropic(**client_args)
 
     @override
diff --git a/tests/strands/models/test_anthropic.py b/tests/strands/models/test_anthropic.py
index c5aff8062..7c9a92aee 100644
--- a/tests/strands/models/test_anthropic.py
+++ b/tests/strands/models/test_anthropic.py
@@ -63,6 +63,38 @@ def test__init__model_configs(anthropic_client, model_id, max_tokens):
     assert tru_temperature == exp_temperature
 
 
+def test__init__sets_user_agent_header(anthropic_client, model_id, max_tokens):
+    _ = anthropic_client
+
+    AnthropicModel(model_id=model_id, max_tokens=max_tokens)
+
+    call_kwargs = strands.models.anthropic.anthropic.AsyncAnthropic.call_args[1]
+    assert "default_headers" in call_kwargs
+    assert "User-Agent" in call_kwargs["default_headers"]
+    assert call_kwargs["default_headers"]["User-Agent"].startswith("strands-agents/")
+
+
+def test__init__preserves_custom_user_agent_header(anthropic_client, model_id, max_tokens):
+    _ = anthropic_client
+
+    custom_headers = {"User-Agent": "my-custom-agent/1.0"}
+    AnthropicModel(model_id=model_id, max_tokens=max_tokens, client_args={"default_headers": custom_headers})
+
+    call_kwargs = strands.models.anthropic.anthropic.AsyncAnthropic.call_args[1]
+    assert call_kwargs["default_headers"]["User-Agent"] == "my-custom-agent/1.0"
+
+
+def test__init__does_not_mutate_caller_headers(anthropic_client, model_id, max_tokens):
+    _ = anthropic_client
+
+    original_headers = {"X-Custom": "value"}
+    client_args = {"default_headers": original_headers}
+    AnthropicModel(model_id=model_id, max_tokens=max_tokens, client_args=client_args)
+
+    assert "User-Agent" not in original_headers
+    assert original_headers == {"X-Custom": "value"}
+
+
 def test_update_config(model, model_id):
     model.update_config(model_id=model_id)