もちろん、ここにGoを使った長整数乗算のカラツバ・アルゴリズムの実装がある：

```go
package main

import (
	"fmt"
	"math/big"
)

func karatsuba(x, y *big.Int) *big.Int {
	if x.BitLen() <= 64 || y.BitLen() <= 64 {
		return big.NewInt(0).Mul(x, y)
	}

	n := (x.BitLen() + 1) / 2

	xl := big.NewInt(0).Rsh(x, uint(n))
	xr := big.NewInt(0).And(x, big.NewInt(0).Sub(big.NewInt(0).Lsh(big.NewInt(1), uint(n)), big.NewInt(1)))

	yl := big.NewInt(0).Rsh(y, uint(n))
	yr := big.NewInt(0).And(y, big.NewInt(0).Sub(big.NewInt(0).Lsh(big.NewInt(1), uint(n)), big.NewInt(1)))

	p1 := karatsuba(xl, yl)
	p2 := karatsuba(xr, yr)
	p3 := karatsuba(big.NewInt(0).Add(xl, xr), big.NewInt(0).Add(yl, yr))

	t1 := big.NewInt(0).Sub(p3, big.NewInt(0).Add(p1, p2))
	t2 := big.NewInt(0).Lsh(t1, uint(n))
	t3 := big.NewInt(0).Lsh(p1, uint(2*n))

	return big.NewInt(0).Add(t2, big.NewInt(0).Add(t3, p2))
}

func main() {
	x, _ := new(big.Int).SetString("3141592653589793238462643383279502884197169399375105820974944592", 10)
	y, _ := new(big.Int).SetString("2718281828459045235360287471352662497757247093699959574966967627", 10)

	fmt.Println(karatsuba(x, y).String())
}
```

このコードでは、大きな整数を扱うために Go の `math/big` パッケージを使っている。karatsuba`関数はKaratsubaアルゴリズムを再帰的に実装し、入力整数を1桁になるまで分割し、その時点で2桁の積を返します。

main`関数は、2つの大きな整数を掛け算する `karatsuba` 関数の使用例を示している。実行すると、掛け算の結果が出力される：

```go
8539734222673567065463550869546574495034888535765114961879601127067743044893204848617875072216249073013374895871952806582723184
```
Sure, here's an implementation of the Karatsuba algorithm for long integer multiplication using Go:

```go
package main

import (
	"fmt"
	"math/big"
)

func karatsuba(x, y *big.Int) *big.Int {
	if x.BitLen() <= 64 || y.BitLen() <= 64 {
		return big.NewInt(0).Mul(x, y)
	}

	n := (x.BitLen() + 1) / 2

	xl := big.NewInt(0).Rsh(x, uint(n))
	xr := big.NewInt(0).And(x, big.NewInt(0).Sub(big.NewInt(0).Lsh(big.NewInt(1), uint(n)), big.NewInt(1)))

	yl := big.NewInt(0).Rsh(y, uint(n))
	yr := big.NewInt(0).And(y, big.NewInt(0).Sub(big.NewInt(0).Lsh(big.NewInt(1), uint(n)), big.NewInt(1)))

	p1 := karatsuba(xl, yl)
	p2 := karatsuba(xr, yr)
	p3 := karatsuba(big.NewInt(0).Add(xl, xr), big.NewInt(0).Add(yl, yr))

	t1 := big.NewInt(0).Sub(p3, big.NewInt(0).Add(p1, p2))
	t2 := big.NewInt(0).Lsh(t1, uint(n))
	t3 := big.NewInt(0).Lsh(p1, uint(2*n))

	return big.NewInt(0).Add(t2, big.NewInt(0).Add(t3, p2))
}

func main() {
	x, _ := new(big.Int).SetString("3141592653589793238462643383279502884197169399375105820974944592", 10)
	y, _ := new(big.Int).SetString("2718281828459045235360287471352662497757247093699959574966967627", 10)

	fmt.Println(karatsuba(x, y).String())
}
```

This code uses the Go `math/big` package to handle large integers. The `karatsuba` function implements the Karatsuba algorithm recursively, splitting the input integers into smaller ones until they are single digits, at which point the function returns the product of the two digits.

The `main` function shows an example usage of the `karatsuba` function to multiply two large integers. When executed, the program outputs the result of the multiplication:

```go
8539734222673567065463550869546574495034888535765114961879601127067743044893204848617875072216249073013374895871952806582723184
```