Draft 0.3 (Concept): this release may have few details, but outlines the general approach and goals. For PCIe 4.0 this included the 16 GT/s signaling rate, re-use of the 128/130 encoding scheme developed for PCI 3.0 8 GT/s mode, maintaining full backwards compatibility, etc. and was released in February 2014.
Draft 0.5 (First draft): this release has a complete set of architectural requirements and must fully address the goals set out in the 0.3 draft. The PCIe 4.0 Draft 0.5 specification was released in February 2015.
Draft 0.7 (Complete draft): this release must have a complete set of functional requirements and methods defined, and no new functionality may be added to the specification after this release. Before the release of this draft, electrical specifications must have been validated via test silicon. For PCIe 4.0, two independent implementations were provided to PCI-SIG workgroup members, one from Synopsys, and the other from Mellanox. The PCIe 4.0 Draft 0.7 was released November 15, 2016.
Draft 0.9 (Final draft): this release allows PCI-SIG member companies to perform an internal review for intellectual property, and no functional changes are permitted after this draft.
1.0 (Final release): this is the final and definitive specification, and any changes or enhancements will be through Errata documentation and Engineering Change Notices (ECNs) respectively.