What should I do with out-of-stock product pages?

The right choice depends on whether the product will return and whether the page has value, such as rankings, traffic or links:

• Temporarily out of stock: keep the URL indexed, show availability clearly, update availability in the Product structured data, offer a back-in-stock alert and link to similar products.
• Discontinued, with a direct replacement: 301 redirect to the new model.
• Discontinued without a replacement, but with links or traffic: keep it as an information page linking to the category, or redirect it to the most relevant category.
• Discontinued with no value: return a 404 or 410, and remove it from internal links and sitemaps.

Avoid redirecting large numbers of unrelated products to the homepage. It frustrates shoppers who expected a specific product, and search engines are unlikely to treat an irrelevant page as a real replacement.

Handle this with rules in your platform rather than one page at a time, so the approach stays consistent as stock changes. On Shopify and WooCommerce that usually means a setting, an app or a small template change, plus a regular check of discontinued products.