diff --git a/.github/prompts/changelog-entries.prompt.yml b/.github/prompts/changelog-entries.prompt.yml
new file mode 100644
index 00000000..f8f47519
--- /dev/null
+++ b/.github/prompts/changelog-entries.prompt.yml
@@ -0,0 +1,52 @@
+messages:
+  - role: system
+    content: |-
+      You write CHANGELOG entries describing an automated API update to slack-ruby-client, a
+      Ruby gem whose Web API endpoint methods, argument validations, specs, and bin commands
+      are code-generated from JSON method definitions vendored from
+      https://github.com/slack-ruby/slack-api-ref (via a git submodule and rake task).
+
+      Given a diffstat and a diff of the regenerated files, respond with a JSON object:
+      {"entries": [string, ...]}
+
+      Rules for entries:
+      - Each entry is a single short line, imperative mood, no leading bullet/dash and no
+        trailing period (the caller adds both).
+      - Group related changes together into one entry per notable change or affected method
+        group (e.g. one entry for "Add chat.appendStream and chat.stopStream methods", one
+        entry for "Add a metadata argument to chat.postEphemeral, chat.postMessage,
+        chat.scheduleMessage, and chat.update"), rather than one entry per file.
+      - Focus on developer-visible API surface changes: new/removed/renamed methods, new/
+        removed/changed arguments (including required/mutually-exclusive validation changes),
+        new/removed error codes, and behavioral changes to generated code.
+      - Skip purely mechanical noise (e.g. reformatted docs/comments with no semantic change).
+      - Produce at most 8 entries. If there are no notable API surface changes, return a single
+        generic entry describing the update in one line.
+  - role: user
+    content: |-
+      Diffstat:
+      {{diff_stat}}
+
+      Diff (may be truncated):
+      {{diff}}
+model: openai/gpt-4o-mini
+responseFormat: json_schema
+jsonSchema: |-
+  {
+    "name": "changelog_entries",
+    "strict": true,
+    "schema": {
+      "type": "object",
+      "properties": {
+        "entries": {
+          "type": "array",
+          "items": {
+            "type": "string"
+          },
+          "description": "1-8 short, imperative-mood CHANGELOG entry descriptions, no leading bullet or trailing period"
+        }
+      },
+      "additionalProperties": false,
+      "required": ["entries"]
+    }
+  }
diff --git a/.github/workflows/update_api.yml b/.github/workflows/update_api.yml
index fe069e48..3eeefc0a 100644
--- a/.github/workflows/update_api.yml
+++ b/.github/workflows/update_api.yml
@@ -10,6 +10,7 @@ jobs:
     permissions:
       contents: write
       pull-requests: write
+      models: read
     steps:
       - uses: actions/checkout@v7
         with:
@@ -32,6 +33,47 @@ jobs:
       - name: Get slack-api-ref ref
         id: api-ref
         run: echo "api-ref=$(git rev-parse --short HEAD:lib/slack/web/api/slack-api-ref)" >> $GITHUB_OUTPUT
+      - name: Check for changes
+        id: changes
+        run: |
+          if git diff --quiet; then
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
+      - name: Prepare diff for AI summary
+        if: steps.changes.outputs.changed == 'true'
+        run: |
+          git diff --stat > /tmp/diff_stat.txt
+          git diff | head -c 20000 > /tmp/diff.txt
+      - name: Generate changelog entries with AI
+        if: steps.changes.outputs.changed == 'true'
+        id: ai
+        uses: actions/ai-inference@v1
+        with:
+          prompt-file: ./.github/prompts/changelog-entries.prompt.yml
+          file_input: |
+            diff_stat: /tmp/diff_stat.txt
+            diff: /tmp/diff.txt
+      - name: Build changelog entries
+        id: entries
+        run: |
+          entries=""
+          if [ "${{ steps.changes.outputs.changed }}" = "true" ]; then
+            entries="$(jq -r '.entries[]? // empty' "${{ steps.ai.outputs.response-file }}" 2>/dev/null)"
+          fi
+          if [ -z "$entries" ]; then
+            entries="Update API from slack-api-ref@${{ steps.api-ref.outputs.api-ref }}"
+          fi
+          body_list="$(printf '%s\n' "$entries" | sed 's/^/- /')"
+          {
+            echo 'entries<<CHANGELOG_ENTRIES_EOF'
+            echo "$entries"
+            echo 'CHANGELOG_ENTRIES_EOF'
+            echo 'body_list<<CHANGELOG_BODY_EOF'
+            echo "$body_list"
+            echo 'CHANGELOG_BODY_EOF'
+          } >> "$GITHUB_OUTPUT"
       - name: GitHub App token
         if: ${{ github.repository == 'slack-ruby/slack-ruby-client' }}
         id: github_app_token
@@ -52,6 +94,10 @@ jobs:
             Update API from [slack-api-ref](https://github.com/slack-ruby/slack-api-ref).
             Rev: ${{ steps.api-ref.outputs.api-ref }}
             Date: ${{ steps.date.outputs.date }}
+
+            ## Changes
+
+            ${{ steps.entries.outputs.body_list }}
           branch: automated-api-update
           base: master
           committer: slack-ruby-ci-bot <noreply@github.com>
@@ -62,12 +108,24 @@ jobs:
           git fetch origin automated-api-update
           git checkout automated-api-update
       - name: Update CHANGELOG
-        uses: jacobtomlinson/gha-find-replace@v3
         if: ${{ steps.cpr.outputs.pull-request-number != '' }}
-        with:
-          include: CHANGELOG.md
-          find: "\\* Your contribution here."
-          replace: "* [#${{steps.cpr.outputs.pull-request-number}}](https://github.com/slack-ruby/slack-ruby-client/pull/${{steps.cpr.outputs.pull-request-number}}): Update API from [slack-api-ref@${{ steps.api-ref.outputs.api-ref }}](https://github.com/slack-ruby/slack-api-ref/commit/${{ steps.api-ref.outputs.api-ref }}) - [@slack-ruby-ci-bot](https://github.com/apps/slack-ruby-ci-bot).\n* Your contribution here."
+        env:
+          PR_NUMBER: ${{ steps.cpr.outputs.pull-request-number }}
+          ENTRIES: ${{ steps.entries.outputs.entries }}
+        run: |
+          ruby - <<'RUBYEOF'
+          pr_number = ENV.fetch("PR_NUMBER")
+          pr_url = "https://github.com/slack-ruby/slack-ruby-client/pull/#{pr_number}"
+          entries = ENV.fetch("ENTRIES").each_line.map(&:strip).reject(&:empty?)
+
+          lines = entries.map do |entry|
+            "* [##{pr_number}](#{pr_url}): #{entry} - [@slack-ruby-ci-bot](https://github.com/apps/slack-ruby-ci-bot)."
+          end.join("\n")
+
+          content = File.read("CHANGELOG.md")
+          content = content.sub("* Your contribution here.", "#{lines}\n* Your contribution here.")
+          File.write("CHANGELOG.md", content)
+          RUBYEOF
       - name: Commit and Push
         if: ${{ steps.cpr.outputs.pull-request-number != '' }}
         run: |
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7a60b654..83b7f8f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ### 3.2.1 (Next)
 
+* [#591](https://github.com/slack-ruby/slack-ruby-client/pull/591): Generate AI CHANGELOG entries and PR summaries for automated API update PRs, lock simplecov below 1.1.0 to avoid breaking Coveralls - [@dblock](https://github.com/dblock).
 * Your contribution here.
 
 ### 3.2.0 (2026/07/05)
diff --git a/Gemfile b/Gemfile
index ccc186e4..5f209263 100644
--- a/Gemfile
+++ b/Gemfile
@@ -21,7 +21,10 @@ group :test do
   gem 'rubocop-performance'
   gem 'rubocop-rake'
   gem 'rubocop-rspec'
-  gem 'simplecov'
+  # Lock below 1.1.0, which started writing float timestamps to
+  # coverage/.resultset.json, breaking coverallsapp/github-action's parser
+  # (coverallsapp/github-action#269, coverallsapp/coverage-reporter#191).
+  gem 'simplecov', '< 1.1.0'
   gem 'simplecov-lcov'
   gem 'timecop'
   gem 'vcr'