diff --git a/reference/runtime-environment.html.md b/reference/runtime-environment.html.md
index 6afe61bfaf..e836b4b322 100644
--- a/reference/runtime-environment.html.md
+++ b/reference/runtime-environment.html.md
@@ -32,6 +32,21 @@ Not to be confused with the [HTTP header](/docs/reference/runtime-environment/#f
 ### `FLY_IMAGE_REF`
 **Docker Image Reference**: The name of the Docker image running this container. Useful if your application needs to launch Machine instances of itself to scale up-or-down. Read about how [a Rails app runs Machines for scale-to-zero background workers](https://fly.io/ruby-dispatch/rails-background-jobs-with-fly-machines/). `registry.fly.io/my-app-name:deployment-01H9RK9EYO9PGNBYAKGXSHV0PH` is an example of the Docker Image Reference's format.
 
+### `FLY_MACHINE_ID`
+**Machine ID**: The unique ID that flyctl commands and the Machines API use to identify a Machine. You can find it in the [logs](/docs/flyctl/logs/).
+
+### `FLY_MACHINE_VERSION`
+**Machine Configuration Version**: The version associated to a specific Machine configuration. When you update a Machine's configuration (including when you update its Docker image), it gets a new `FLY_MACHINE_VERSION`. You can also find this value under the name `Instance ID` in the output of `fly machine status`. Changing the Machine's metadata however doesn't trigger a new version.
+
+### `FLY_PRIVATE_IP`
+**Private IPv6 Address**: The IPv6 address of the Machine on its [6PN private network](/docs/reference/private-networking/).
+
+### `FLY_PROCESS_GROUP`
+**Process Group**: The [process group](/docs/apps/processes) associated with the Machine. 
+
+### `FLY_VM_MEMORY_MB`
+**Machine Memory**: The memory allocated to the Machine, in MB. It's the same value you'll find under https://fly.io/dashboard/personal/machines and VM Memory in the output of `fly machine status`. Learn more about [Machine sizing](/docs/machines/guides-examples/machine-sizing/).
+ 
 ## _Request Headers_
 
 ### `Fly-Client-IP`