diff --git a/extensions/deltas.md b/extensions/deltas.md
deleted file mode 100644
index 159430f0..00000000
--- a/extensions/deltas.md
+++ /dev/null
@@ -1,26 +0,0 @@
-# Deltas
-
-The following definition of the `stacks` field in `buildpack.toml` extends the [Data Format - buildpack.toml (TOML)](../buildpack.md#buildpack.toml-(toml)) section of the Buildpack Interface Specification.
-
-```toml
-[[stacks]]
-id = "<stack ID>"
-build-images = ["<build image tag>"]
-run-images = ["<run image tag>"]
-run-delta = "path/to/run.Dockerfile"
-build-delta = "path/to/build.Dockerfile"
-```
-
-The `run-delta` and `build-delta` fields MUST contain paths to idempotent Dockerfiles if present.
-These Dockerfiles MUST accept `stack` as a build argument, and SHOULD use `FROM $stack` to receive the argument.
-These Dockerfiles MUST add the label `io.buildpacks.delta.<buildpack ID>@<buildpack version>` with any non-empty value to the OCI image config.
-
-A platform MAY create a builder image by extending a stack build image with a buildpacks directory as specified in the [Buildpacks - Buildpacks Directory Layout](../platform.md#buildpacks-directory-layout) section of the Platform Interface Specification.
-This builder image MUST be generated by successively applying the `build-delta` Dockerfiles from each included buildpack in succession before the buildpacks directory is added.
-Additionally, an extended run image MUST be generated by successively applying the `run-delta` Dockerfiles from each included buildpack in succession.
-
-App and launch layers generated using the builder image MUST be applied to the corresponding extended run image.
-When a new run image is available, those layers SHOULD be rebased on the extended run image.
-They MUST NOT be rebased on the original stack run image without `run-delta` modifications.
-
-These build and run images SHOULD be treated as stack images and SHOULD be regenerated when new stack images are available.