The artificer class has been published in several different articles that aren't well connected and have several confusing differences between them. It's really confusing when others talk about Artificer subclasses that don't appear in the version that you are familiar with.
Therefore: what is the release history of the Artificer class for D&D 5e? What are the major differences between the releases?
The goal with this Q&A is to put this information available in one place, to be used as a pointer and to help identify which version someone is working from.
Best Answer
Class Playtesting
Prior to being its own class, the artificer premiered as a wizard subclass in the 2015 UA: Eberron (article, pdf).
The first version of the Artificer proper was published at the start of 2017 (article, pdf). In this first they were a 1/3 spellcaster (same progression as an Eldritch Knight or Arcane Trickster), chose several magic items as part of their level progression and had two subclasses; Alchemist and Gunsmith.
The second iteration came early 2019 (article, pdf). The class was now rescaled to 1/2 casting (same spell progression as Paladins and Rangers), got magic items as Infusions and had Alchemist and Artillerist as subclasses. This version also introduced a class unique spell: arcane weapon.
In May of the same year, the third iteration was published (article, pdf). This version made little to no changes to the base class, but introduced two new subclasses: Archivist and Battle Smith, updated the spell list, added some new infusions, and tweaked the multiclassing rule (see article for more).
Release
Then in November of 2019 Eberron: Rising from the Last War was released. This book contained the finalised version of the class (p. 54). The notable changes from the last iteration are:
In additional to release in Eberron: Rising from the Last War, the base class and the Alchemist subclass was added as Appendix D to the living document Wayfinder's Guide to Eberron.
Post Release
In February 2020 (article, pdf) a new subclass—the Armorer—appeared for playtesting.
That same subclass was later published with minor revisions, along with the base class and all three previous subclasses, in Tasha's Cauldron of Everything on the 17th of November 2020, along with a handful of new infusions.