Deno was announced in 2018, and then it went into development for almost two years. The first version of Deno that came out in the summer of 2020 contained most of the toolchain as well. After almost two years of breakneck development, the first public release of Deno happened on May 13, 2020. This was 1.0.0, a major milestone. There were bugs, of course. But Deno worked well. After that, Deno stuck to a regular schedule of major releases.
The development and release of Deno still happen at a breakneck speed. The Deno repository on Github is very active. Multiple check-ins happen almost daily. Here is a month-long insight from GitHub at the time of writing (Nov-Dec 2020):
Excluding merges, 51 authors have pushed 173 commits to master and 173 commits to all branches. On master, 447 files have changed and there have been 33,087 additions and 16,234 deletions.
This is a major development.
The major releases like 1.1.0, 1.2.0, 1.3.0, etc. happen approximately at a monthly frequency.
The minor releases happen between 2-8 days. Unless there is an urgent issue which demands a minor release, a weekly schedule is followed for normal minor releases.
Deno is changing fast, very fast. A large number of features and bug fixes go into each of the major and minor releases. It'd reach stability sometime soon, then the development speed should reduce, hopefully.
Here are some details about all five major releases that happened since the first public release.
June 12, 2020
July 13, 2020
August 13, 2020
September 13, 2020
October 27, 2020
December 8, 2020
There are many enhancements and fixes that go in each of the releases (whether major or minor). It gets tough to list all the changes as there are too many of them.
The official release notes are here: https://github.com/denoland/deno/releases. As can be seen from the release notes, though it'd look like Deno is moving fast, there wasn't way too many major feature additions. Most of the stuff getting into releases from 1.1 to 1.5 is relatively minor. These are small enhancements and a large number of bug fixes.