Add blog entry for sunsetting IDF 4.x support (#39)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

Author: kbx81

docs/blog/posts/2025-06-14-sunsetting-idf-4.md

@@ -0,0 +1,48 @@
+---
+date: 2025-06-18
+authors: 
+  - kbx81
+comments: true
+---
+
+# Sunsetting support for IDF 4.x
+
+At the beginning of this year, we made the transition from IDF 4.4 to IDF 5.1; this was a major upgrade and many
+changes were necessary within ESPHome to achieve this.
+
+A long-standing (but largely undocumented -- until now) rule of the project is that we only support one major version
+of [ESP-IDF](https://github.com/espressif/esp-idf) at a time. While it's technically _possible_ to support multiple
+major versions, doing so introduces some significant challenges:
+
+- Code is more messy, complex and difficult to maintain
+- Changes are more complex to test
+- CI run durations are (significantly) longer
+
+As you may know, ESPHome supports using both [ESP-IDF](https://github.com/espressif/esp-idf) and
+[Arduino](https://www.arduino.cc) as frameworks for projects built with Espressif's ESP32 family of microcontrollers.
+Up to this point, we have been using Arduino 2.x, which is built on IDF 4.x; this effectively means we are still using
+(and supporting) two different major versions of IDF. In the next release of ESPHome, we'll update the default Arduino
+framework version to 3.x, which is built on IDF 5.x; this means we will no longer need to maintain compatibility with
+IDF 4.x.
+
+Just prior to switching the default IDF version to 5.1, we were running our tests against both major versions -- but
+this meant that our CI took over ten hours to complete for one single release! This isn't tenable in the long term and,
+after making IDF 5.1 the default, we stopped running our tests against IDF 4.x in an effort to get our CI run duration
+back down to "normal"...which is still often over five hours now. (We are looking for ways to improve this, but that's
+a topic for another day.)
+
+Beyond this, maintaining a codebase with support for both major versions is just plain messy and complex. As Espressif
+releases more and more new SoCs/microcontrollers, support for them won't be backported into IDF 4.x, which means that
+you won't be able to use those new microcontrollers with IDF 4.x, anyway. Further, as new features and functionality
+are introduced into IDF 5.x, they also won't be backported to IDF 4.x, so you won't be able to take advantage of these.
+
+Last, but not least, we've made a number of optimizations to reduce the memory (RAM and flash) footprint of ESPHome
+in this (June) release; if you were experiencing issues with IDF 5.x before, please try it again as you're more likely
+to be able to use it now.
+
+With these points in mind, we are officially sunsetting support for IDF 4.x in ESPHome. If you have kept your
+project(s) back on IDF 4.x, you can continue to use versions of ESPHome prior to the July 2025 release, but you won't
+be able to upgrade beyond that version. We encourage everybody to move to IDF 5.x -- specifically, in the June release,
+we have switched the default IDF version to 5.3.2. In addition, we'd like to call out that we are working to accelerate
+the adoption of new IDF versions; this helps us add support for new Espressif microcontrollers more quickly than we've
+been able to in the past.