Shopify SKU Lookup using GraphQL

Question

I have a Query i have been using, but today i have noticed and issue where the SKU appears to be searching a wild card opposed to just the SKU Field. I suspect its the format of my query, as if i modify it slightly i can make it work correctly.

GraphQL Query:

query ($first: Int, $sku: String)
{ productVariants(first: $first, query: $sku) {
    edges {
      node {
        title
        id
        sku
        product {
          title
        }
        inventoryItem {
          id
          inventoryLevels(first: 3) {
            edges {
              node {
                id
                available
                location {
                  id
                  name
                  address {
                    city
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Variables

{
  "first": 5,  
  "sku": "555"
}

So when searching 555 SKU its actually returning products that have 555 in the body_html.

If i edit the query to have the SKU Embedded then it works, but i need to use it with a variable, maybe its my poorly formatted query.

Edited the Query as follow to embed the sku in the query and it works.

query ($first: Int)
{ productVariants(first: $first, query: "sku:555") {
    edges {
      node {
        title
        id
        sku
        product {
          title
        }
        inventoryItem {
          id
          inventoryLevels(first: 3) {
            edges {
              node {
                id
                available
                location {
                  id
                  name
                  address {
                    city
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

How does one format it so it shows like:

 query: "sku:"$sku