Versions of AutoCAD

DWG Versions

AutoDesk does not change the AutoCAD Drawing File Format nearly as frequently as it releases new versions, at least recently. In the early days the DWG file format was changing with pretty much every release, but while the format change for AutoCAD 2013, it did not change again until AutoCAD 2018, despite yearly releases of the program. So, the same file format was used for AutoCAD 2013, AutoCAD 2014, AutoCAD 2015, AutoCAD 2016 and AutoCAD 2017. Similarly, the format is identical for AutoCAD 2018, AutoCAD 2019 and AutoCAD 2020.

It is easy to decipher what version of AutoCAD created a given drawing file. Open the file in a text editor and look at the first six bytes (five in very early files) and match them to the following list. For DXF files this tag is given by the $ACADVER variable in the header. For instance, if the first five bytes are AC1.2 then it was created by the ancient (April 1983, so more than 35 years ago) AutoCAD Version 1.2 (or maybe AutoCAD Version 1.3, things get a little spotty back that far). If the first six bytes are AC1009 then it was created by either AutoCAD Release 11 or AutoCAD Release 12 as they shared the same format version.

If the DWG Tag value is bold in the table that means the file format changed for that version. Otherwise the file format stayed the same as in the previous version.

BTW: LinkList 2025 can support any version of DWG and DXF back to AutoCAD 2.5. The format changed greatly at that point and we know of no programs that support older formats. However, that was June of 1986, so the likelihood of seeing a 33+ year old AutoCAD Version 2.22 or before file is remote at best.