diff --git a/README.md b/README.md
index d42bf90..0c9c555 100644
--- a/README.md
+++ b/README.md
@@ -112,6 +112,13 @@ GPTC.
 
 See `models/unpacked/` for an example of the format.
 
+### `gptc.Classifier(model, max_ngram_length=1)`
+
+`Classifier` objects are deprecated starting with GPTC 3.1.0, and will be
+removed in 5.0.0. See [the README from
+3.0.2](https://git.kj7rrv.com/kj7rrv/gptc/src/tag/v3.0.1/README.md) if you need
+documentation.
+
 ## Ngrams
 
 GPTC optionally supports using ngrams to improve classification accuracy. They