For statements with for clause

… Any element of the ForClause may be empty but the semicolons are required unless there is only a condition. If the condition is absent, it is equivalent to the boolean value true.

for cond { S() }    is the same as    for ; cond ; { S() }
for      { S() }    is the same as    for true     { S() }

So this goes to show that the single condition form of the for loop is really just a special case of the “for clause” for loop, with the init and post statements omitted.

But let’s look at some other examples of omitting elements of the for clause. These are all valid:

for x := 0; ; { // Initialize variable x, then start an infinite* loop

for ; x < 3; { // Same as `for x < 3 {`

for ; ; x++ { // Increments x after every iteration of the looop

for x := 0; ; x++ { // Initializes variable x, then increments it after every iteration of the infinite* loop

for ; ; { // Same as `for true {` or `for {`

*such loops can still be terminated by a terminating statement such as break or return.

Quotes from The Go Programming Language Specification Language version go1.22 (Feb 6, 2024)