diff --git a/.github/workflows/test-breaking.yaml b/.github/workflows/test-breaking.yaml
index f5a6e22..80fc579 100644
--- a/.github/workflows/test-breaking.yaml
+++ b/.github/workflows/test-breaking.yaml
@@ -277,3 +277,67 @@ jobs:
             echo "Expected 'No breaking changes' (err-ignore from .oasdiff.yaml should suppress findings) but got '$output'" >&2
             exit 1
           fi
+
+  oasdiff_breaking_yaml_config_severity_levels:
+    runs-on: ubuntu-latest
+    name: Test breaking action picks up severity-levels from .oasdiff.yaml
+    steps:
+      - name: checkout
+        uses: actions/checkout@v7
+      # specs/severity-levels.txt downgrades api-removed-without-deprecation to
+      # info, so the one breaking change these specs produce stops being an
+      # error and fail-on: ERR no longer fails the step.
+      - name: Drop .oasdiff.yaml at repo root
+        run: |
+          cat > .oasdiff.yaml <<EOF
+          severity-levels: specs/severity-levels.txt
+          fail-on: ERR
+          EOF
+      - name: Running breaking action
+        id: test_yaml_severity_levels
+        uses: ./breaking
+        with:
+          base: 'specs/base.yaml'
+          revision: 'specs/revision-breaking.yaml'
+      - name: Assert the finding was downgraded by .oasdiff.yaml
+        run: |
+          delimiter=$(cat /proc/sys/kernel/random/uuid | tr -d '-')
+          output=$(cat <<-$delimiter
+          ${{ steps.test_yaml_severity_levels.outputs.breaking }}
+          $delimiter
+          )
+          if [ "$output" != "No breaking changes" ]; then
+            echo "Expected 'No breaking changes' (severity-levels from .oasdiff.yaml should downgrade the finding to info) but got '$output'" >&2
+            exit 1
+          fi
+
+  oasdiff_breaking_include_checks_deprecated:
+    runs-on: ubuntu-latest
+    name: Test include-checks is warned about, not applied
+    env:
+      OASDIFF_ACTION_TEST_EXPECTED_OUTPUT: "1 changes: 1 error, 0 warning, 0 info"
+    steps:
+      - name: checkout
+        uses: actions/checkout@v7
+      # include-checks is ignored by oasdiff. The action must not pass it on and
+      # must not change the result; it only warns. Passing a name that is not a
+      # real check would fail the run if the action still forwarded it.
+      - name: Running breaking action with include-checks
+        id: test_include_checks
+        continue-on-error: true
+        uses: ./breaking
+        with:
+          base: 'specs/base.yaml'
+          revision: 'specs/revision-breaking.yaml'
+          include-checks: 'not-a-real-check'
+      - name: Assert the run was unaffected
+        run: |
+          delimiter=$(cat /proc/sys/kernel/random/uuid | tr -d '-')
+          output=$(cat <<-$delimiter
+          ${{ steps.test_include_checks.outputs.breaking }}
+          $delimiter
+          )
+          if [ "$output" != "$OASDIFF_ACTION_TEST_EXPECTED_OUTPUT" ]; then
+            echo "Expected output '$OASDIFF_ACTION_TEST_EXPECTED_OUTPUT' (include-checks must be ignored, not forwarded) but got '$output'" >&2
+            exit 1
+          fi
diff --git a/README.md b/README.md
index 4161d01..f07b2b6 100644
--- a/README.md
+++ b/README.md
@@ -99,7 +99,7 @@ jobs:
 | `base` | — (required) | Path to the base (old) OpenAPI spec | file path, URL, git ref |
 | `revision` | — (required) | Path to the revised (new) OpenAPI spec | file path, URL, git ref |
 | `fail-on` | `''` | Fail with exit code 1 if changes are found at or above this severity | `ERR`, `WARN` |
-| `include-checks` | `''` | Include optional breaking change checks | check names (comma-separated) |
+| `include-checks` | `''` | **Deprecated and ignored.** oasdiff retired the optional-checks mechanism; set `severity-levels` in `.oasdiff.yaml` instead. Setting it emits a warning annotation and has no effect | — |
 | `include-path-params` | `false` | Include path parameter names in endpoint matching | `true`, `false` |
 | `deprecation-days-beta` | `31` | Minimum sunset period (days) for deprecation of beta API endpoints | integer |
 | `deprecation-days-stable` | `180` | Minimum sunset period (days) for deprecation of stable API endpoints | integer |
@@ -237,6 +237,15 @@ exclude-elements:
   - title
   - summary
 err-ignore: ./oasdiff-err-ignore.txt
+severity-levels: ./oasdiff-levels.txt
+```
+
+`severity-levels` points at a file that overrides the severity of individual checks, one `check-id level` per line, where level is `err`, `warn`, `info` or `none`. Raise a check to `err` (with `fail-on: ERR`) to make it fail the build, or set it to `none` to silence it:
+
+```
+# oasdiff-levels.txt
+api-version-not-bumped          err
+api-major-version-not-bumped    err
 ```
 
 The actions read this file from the runner's `$GITHUB_WORKSPACE` (which `actions/checkout` populates), so no extra steps are needed.
diff --git a/breaking/action.yml b/breaking/action.yml
index 4d81572..d5c3bff 100644
--- a/breaking/action.yml
+++ b/breaking/action.yml
@@ -12,7 +12,7 @@ inputs:
     required: false
     default: ''
   include-checks:
-    description: 'Include any of the defined optional breaking changes checks'
+    description: 'Deprecated and ignored: oasdiff retired the optional-checks mechanism. To make a check fail the build, set severity-levels in .oasdiff.yaml.'
     required: false
   include-path-params:
     description: 'Include path parameter names in endpoint matching'
diff --git a/breaking/entrypoint.sh b/breaking/entrypoint.sh
index 00dac9a..a636528 100755
--- a/breaking/entrypoint.sh
+++ b/breaking/entrypoint.sh
@@ -148,7 +148,7 @@ if [ "$include_path_params" = "true" ]; then
     flags="$flags --include-path-params"
 fi
 if [ -n "$include_checks" ]; then
-    flags="$flags --include-checks $include_checks"
+    echo "::warning::oasdiff: 'include-checks' is ignored, the optional-checks mechanism it drove was retired. To make a check fail the build, add 'severity-levels: <file>' to .oasdiff.yaml, listing the check id with level 'err', and set 'fail-on: ERR'."
 fi
 if [ -n "$deprecation_days_beta" ]; then
     flags="$flags --deprecation-days-beta $deprecation_days_beta"
diff --git a/specs/severity-levels.txt b/specs/severity-levels.txt
new file mode 100644
index 0000000..511bf82
--- /dev/null
+++ b/specs/severity-levels.txt
@@ -0,0 +1 @@
+api-removed-without-deprecation	info