How do I grab the current product SKU in code, as early as possible? In Drupal Commerce, using programming, what is the way to grab the product SKU of the product entity that is about to fire off and display on the page in a product display node, as early as possible?  I'm looking for something that is before panes and views are executed and drawn.

I know the SKU lives in $form_state['default_product']->sku within a hook_form_alter, but that is too late.

In panels, I know there is a time in hook_panels_pane_content_alter where I can scrape the SKU out of $content->content['#markup'].  That doesn't seem to update though as I change the selectors that affect which product is currently displaying.  So that's no good.

I need it as early as possible, because I want to pass that value into a view during hook_views_pre_view, which is executed very early.
Have you tried using menu_get_object?  It provides access to objects loaded by the current router item.

Once you've got the node, the product reference field is just going to list the products and Drupal Commerce may exclude products from the add to cart form based on rules and other modules.  But you can get the SKU of the first referenced product on the product display like this: 

$node = menu_get_object(); // May want to check that it's a node.
$node = entity_metadata_wrapper('node', $node);
$products = $node-&gt;field_product-&gt;get(0)-&gt;sku-&gt;value(); // field_product is my product reference, may want to check that it exists.