Minecraft wiki entry for Development_versions, associated text: The day before Beta 1.6 was released, Mojang created a Test Build version that was never released, but was nonetheless a development version for Beta 1.6. Between Beta 1.7.3 and Beta 1.8, Mojang began to issue pre-release versions, specifically for Beta 1.8 and what then was known as Beta 1.9. As Beta 1.9 came to be re-designated as release version 1.0.0, candidates subject to release were designated with the prefix "RC#".