Why do I have the 2.80 API on blender 2.79 When I compare the latest blender api to the 2.79b API (based on the current link from https://docs.blender.org/api/), I see that the bake_action API changed from accepting start_frame and end_frame to taking a single frames iterable.

When I run blender --version, I get:

Blender 2.79 (sub 6)
        build date: 2018-12-25
        build time: 20:34:04
        build commit date: 2018-12-22
        build commit time: 14:10
        build hash: 2c0c1f494dcf
        build platform: Linux
        build type: Release


However, when invoking bpy_extras.anim_utils.bake_action, I get:

  File "/usr/share/blender/2.79/scripts/addons/io_scene_godot/converters/animation/constraint_baking.py", line 87, in bake_constraint_to_action
    do_visual_keying=True,
TypeError: bake_action() missing 1 required keyword-only argument: 'frames'


This suggests that I have the 2.80 API, even though I seem to be on blender 2.79.
What am I misunderstanding about blender versions?
Blender version 2.79b is the one that you can download when you click Download Blender at the top of the download page at https://www.blender.org/download/ at the time I am writing this (05-01-2019). 

If you however choose to scroll down to the bottom of that page and click the red button 'Latest Experimental Builds' in the section with the red background and a clear disclaimer in English: 

 you will be downloading experimental builds (not unlike the disclaimer states) and may try latest changes that may include changes to the Python API.