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int64 is a built-in, statically typed, signed integer data type in Go that occupies exactly 64 bits (8 bytes) of memory, guaranteeing a fixed size regardless of the underlying hardware architecture or operating system. Unlike the architecture-dependent int type, whose size is statically determined at compile time to be either 32 or 64 bits based on the target architecture (GOARCH), int64 provides strict deterministic memory allocation.

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Technical Specifications

  • Memory Footprint: 64 bits (8 bytes)
  • Encoding: Two’s complement representation
  • Sign Bit: The Most Significant Bit (MSB) determines the sign (0 for positive, 1 for negative)
  • Minimum Value: −263-2^{63} (-9,223,372,036,854,775,808)
  • Maximum Value: 263−12^{63}-1 (9,223,372,036,854,775,807)
  • Zero Value: 0

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Syntax and Initialization

You can declare an int64 using standard variable declaration, short variable declaration with explicit type conversion, or the new keyword. 
package main

import "fmt"

func main() {
    // Standard declaration (initialized to zero value)
    var a int64

    // Declaration with initialization
    var b int64 = 9223372036854775807

    // Short declaration using explicit type conversion
    c := int64(-9223372036854775808)

    // Pointer to an int64
    d := new(int64) 

    fmt.Println(a, b, c, *d)
}

​
Boundary Constants

The standard library’s math package provides predefined untyped constants for the absolute boundaries of an int64. 
package main

import (
    "fmt"
    "math"
)

func main() {
    var min int64 = math.MinInt64
    var max int64 = math.MaxInt64

    fmt.Printf("Min: %d, Max: %d\n", min, max)
}

​
Strict Type Resolution and Conversion

Go’s type system does not support implicit type coercion. The compiler treats int64 as a fundamentally distinct type from int, int32, or uint64, even if the underlying architecture is 64-bit (where int and int64 share the same memory footprint). Operations mixing int64 with other numeric types require explicit type conversion. 
package main

import "fmt"

func main() {
    var archInt int = 42
    var fixedInt int64 = 100

    // INVALID: Mismatched types
    // result := archInt + fixedInt 

    // VALID: Explicit type conversion to int64
    result := int64(archInt) + fixedInt

    // VALID: Explicit type conversion to int
    result2 := archInt + int(fixedInt)
    
    fmt.Println(result, result2)
}

​
Overflow Behavior

If an arithmetic operation exceeds the maximum or minimum bounds of int64, Go silently wraps around using two’s complement arithmetic. It does not panic or throw an overflow exception at runtime. 
package main

import (
    "fmt"
    "math"
)

func main() {
    var max int64 = math.MaxInt64
    fmt.Println(max)     // 9223372036854775807

    // Silent overflow wraps to the minimum value
    overflow := max + 1  
    fmt.Println(overflow) // -9223372036854775808
}
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