On November 10, 2009, the Go programming language went public as an open source project from Google. The Go FAQ states plainly that “Go became a public open source project on November 10, 2009,” after roughly two years of internal design and implementation work that had begun in late 2007.
The date is confirmed by Go’s own anniversary writing. The Go blog post “The Go Programming Language turns two,” published on November 10, 2011, opens by recalling that “two years ago a small team at Google went public with their fledgling project — the Go Programming Language,” placing the original release exactly two years earlier.
That release opened the language, compiler, and tools to outside contributors and marked the start of Go’s public history. From this point the project grew from a Google research effort into a widely adopted open source language for systems and infrastructure software.