Amazon has released a host of new features recently and one of them is a new version of what was formerly called "Bid+". This feature is called placement-level bidding and this article gives you an overview of what it means and how it works.
What is placement-level bidding?
Placement level bidding is a new feature that allows you to increase bids based upon where you want ads to appear and replaces what was formerly called "Bid+". Placements include:
Top of Search (first page)
Product pages
Rest of search
What does this look like in Seller Central?
You can opt into placement-level bidding for a particular campaign within campaign settings in Campaign Manager.

What's the benefit of using placement-level bidding?
Placement-level bidding allows you to increase your bids by 0-900% to get placed Top of Search or on Product pages.
What are the impacts of using Placement-level bidding?
Sellers implementing placement-level bidding need to be aware of the following:
There’s no guidance on how high to set the boost. For example, if you boosted ‘Top of Search’ by 100% then you’d need to believe that it performed 2x better than anything else. However, there is no way for you to determine this given current reporting
Amazon does not know your ROAS targets or margins and can thus end up overbidding or underbidding
You risk overbidding since the bids only increase and don't decrease
Sponsored Brands maybe a better use of your funds as it has better placement even than “Top of Search”
How does placement-level bidding work with Flywheel?
Just like Bid+, we recommend leaving placement-level bidding off if you are using Flywheel to automate your campaigns, especially if you are concerned with profitability and are unwilling to spend above a certain MACS. Implementing placement-level bidding can interfere with Flywheel algorithms and give you sub-optimal results.