diff --git a/libs/core/langchain_core/messages/content_blocks.py b/libs/core/langchain_core/messages/content_blocks.py
index 57c72907ea9..727e2cd1085 100644
--- a/libs/core/langchain_core/messages/content_blocks.py
+++ b/libs/core/langchain_core/messages/content_blocks.py
@@ -8,51 +8,6 @@ This module provides a standardized data structure for representing inputs to an
 outputs from LLMs. The core abstraction is the **Content Block**, a ``TypedDict`` that
 can represent a piece of text, an image, a tool call, or other structured data.
 
-Data **not yet mapped** to a standard block may be represented using the
-``NonStandardContentBlock``, which allows for provider-specific data to be included
-without losing the benefits of type checking and validation.
-
-Furthermore, provider-specific fields **within** a standard block are fully supported
-by default. However, since current type checkers do not recognize this, we are temporarily
-applying type ignore comments to suppress warnings. In the future,
-`PEP 728 <https://peps.python.org/pep-0728/>`__ will add an extra param, ``extra_items=Any``.
-When this is supported, we will apply it to block signatures to signify to type checkers
-that additional provider-specific fields are allowed.
-
-**Example with PEP 728 provider-specific fields:**
-
-.. code-block:: python
-
-    # Note `extra_items=Any`
-    class TextContentBlock(TypedDict, extra_items=Any):
-        type: Literal["text"]
-        id: NotRequired[str]
-        text: str
-        annotations: NotRequired[list[Annotation]]
-        index: NotRequired[int]
-
-.. code-block:: python
-
-    from langchain_core.messages.content_blocks import TextContentBlock
-
-    my_block: TextContentBlock = {
-        # Add required fields
-        "type": "text",
-        "text": "Hello, world!",
-        # Additional fields not specified in the TypedDict
-        # These are valid with PEP 728 and are typed as Any
-        "openai_metadata": {"model": "gpt-4", "temperature": 0.7},
-        "anthropic_usage": {"input_tokens": 10, "output_tokens": 20},
-        "custom_field": "any value",
-    }
-
-    openai_data = my_block["openai_metadata"]  # Type: Any
-
-.. note::
-    PEP 728 is enabled with ``# type: ignore[call-arg]`` comments to suppress warnings
-    from type checkers that don't yet support it. The functionality works correctly
-    in Python 3.13+ and will be fully supported as the ecosystem catches up.
-
 **Rationale**
 
 Different LLM providers use distinct and incompatible API schemas. This module
@@ -64,6 +19,62 @@ sequence.
 An adapter for a specific provider is responsible for translating this standard list of
 blocks into the format required by its API.
 
+**Extensibility**
+
+Data **not yet mapped** to a standard block may be represented using the
+``NonStandardContentBlock``, which allows for provider-specific data to be included
+without losing the benefits of type checking and validation.
+
+Furthermore, provider-specific fields **within** a standard block are fully supported
+by default in the ``extras`` field of each block. This allows for additional metadata
+to be included without breaking the standard structure.
+
+Following widespread adoption of `PEP 728 <https://peps.python.org/pep-0728/>`__, we will add
+``extra_items=Any`` as a param to Content Blocks. This will signify to type checkers
+that additional provider-specific fields are allowed outside of the ``extras`` field,
+and that will become the new standard approach to adding provider-specific metadata.
+
+.. warning::
+    Do not heavily rely on the ``extras`` field for provider-specific data! This field
+    is subject to deprecation in future releases as we move towards PEP 728.
+
+**Example with PEP 728 provider-specific fields:**
+
+.. code-block:: python
+
+    # Content block definition
+    # NOTE: `extra_items=Any`
+    class TextContentBlock(TypedDict, extra_items=Any):
+        type: Literal["text"]
+        id: NotRequired[str]
+        text: str
+        annotations: NotRequired[list[Annotation]]
+        index: NotRequired[int]
+
+.. code-block:: python
+
+    from langchain_core.messages.content_blocks import TextContentBlock
+
+    # Create a text content block with provider-specific fields
+    my_block: TextContentBlock = {
+        # Add required fields
+        "type": "text",
+        "text": "Hello, world!",
+        # Additional fields not specified in the TypedDict
+        # These are valid with PEP 728 and are typed as Any
+        "openai_metadata": {"model": "gpt-4", "temperature": 0.7},
+        "anthropic_usage": {"input_tokens": 10, "output_tokens": 20},
+        "custom_field": "any value",
+    }
+
+    # Mutating an existing block to add provider-specific fields
+    openai_data = my_block["openai_metadata"]  # Type: Any
+
+.. note::
+    PEP 728 is enabled with ``# type: ignore[call-arg]`` comments to suppress warnings
+    from type checkers that don't yet support it. The functionality works correctly
+    in Python 3.13+ and will be fully supported as the ecosystem catches up.
+
 **Key Block Types**
 
 The module defines several types of content blocks, including:
@@ -100,6 +111,12 @@ The module defines several types of content blocks, including:
             mime_type="image/png",
         ),
     ]
+
+Factory functions like ``create_text_block`` and ``create_image_block`` are provided
+and offer benefits such as:
+- Automatic ID generation (when not provided)
+- No need to manually specify the ``type`` field
+
 """  # noqa: E501
 
 import warnings
@@ -237,7 +254,7 @@ class TextContentBlock(TypedDict):
     """Block text."""
 
     annotations: NotRequired[list[Annotation]]
-    """Citations and other annotations."""
+    """``Citation``s and other annotations."""
 
     index: NotRequired[int]
     """Index of block in aggregate response. Used during streaming."""
@@ -900,29 +917,29 @@ def is_data_content_block(block: dict) -> bool:
 
 
 def is_tool_call_block(block: ContentBlock) -> TypeGuard[ToolCall]:
-    """Type guard to check if a content block is a tool call."""
+    """Type guard to check if a content block is a ``ToolCall``."""
     return block.get("type") == "tool_call"
 
 
 def is_tool_call_chunk(block: ContentBlock) -> TypeGuard[ToolCallChunk]:
-    """Type guard to check if a content block is a tool call chunk."""
+    """Type guard to check if a content block is a ``ToolCallChunk``."""
     return block.get("type") == "tool_call_chunk"
 
 
 def is_text_block(block: ContentBlock) -> TypeGuard[TextContentBlock]:
-    """Type guard to check if a content block is a text block."""
+    """Type guard to check if a content block is a ``TextContentBlock``."""
     return block.get("type") == "text"
 
 
 def is_reasoning_block(block: ContentBlock) -> TypeGuard[ReasoningContentBlock]:
-    """Type guard to check if a content block is a reasoning block."""
+    """Type guard to check if a content block is a ``ReasoningContentBlock``."""
     return block.get("type") == "reasoning"
 
 
 def is_invalid_tool_call_block(
     block: ContentBlock,
 ) -> TypeGuard[InvalidToolCall]:
-    """Type guard to check if a content block is an invalid tool call."""
+    """Type guard to check if a content block is an ``InvalidToolCall``."""
     return block.get("type") == "invalid_tool_call"
 
 
@@ -1009,7 +1026,7 @@ def create_text_block(
     Args:
         text: The text content of the block.
         id: Content block identifier. Generated automatically if not provided.
-        annotations: Citations and other annotations for the text.
+        annotations: ``Citation``s and other annotations for the text.
         index: Index of block in aggregate response. Used during streaming.
 
     Returns: