diff --git a/.env.example b/.env.example
index af492e576..3e81fbc7a 100644
--- a/.env.example
+++ b/.env.example
@@ -26,6 +26,7 @@ REDIS_DB=0
 REDIS_PASSWORD=
 
 CACHE_DRIVER=file
+CACHE_API_RESPONSE_SUMMIT_DATES_WITH_EVENTS_LIFETIME=300
 
 SESSION_DRIVER=redis
 SESSION_COOKIE_DOMAIN=
diff --git a/app/ModelSerializers/Summit/SummitSerializer.php b/app/ModelSerializers/Summit/SummitSerializer.php
index 564e6d342..7002614cb 100644
--- a/app/ModelSerializers/Summit/SummitSerializer.php
+++ b/app/ModelSerializers/Summit/SummitSerializer.php
@@ -198,7 +198,6 @@ class SummitSerializer extends SilverStripeSerializer
         'badge_types',
         'badge_features_types',
         'badge_access_level_types',
-        'dates_with_events',
         'supported_currencies',
     ];
 
diff --git a/app/Models/Foundation/Summit/Summit.php b/app/Models/Foundation/Summit/Summit.php
index f2a7dfc41..756245a50 100644
--- a/app/Models/Foundation/Summit/Summit.php
+++ b/app/Models/Foundation/Summit/Summit.php
@@ -6024,39 +6024,69 @@ public function getSummitDays(): array
     public function getSummitDaysWithEvents(): array
     {
         $days = $this->getSummitDays();
-        $list = [];
-        foreach ($days as $day) {
-            $begin = clone($day);
-            $begin = $begin->setTime(0, 0, 0)->setTimezone(new \DateTimeZone('UTC'));
-            $end = clone($day);
-            $end = $end->setTime(23, 59, 59)->setTimezone(new \DateTimeZone('UTC'));
-            $count = 0;
-            try {
-                $sql = <<<SQL
-            SELECT COUNT(SummitEvent.ID) AS QTY
+        if (count($days) == 0) return [];
+
+        $lifetime = intval(Config::get('cache_api_response.summit_dates_with_events_lifetime', 0));
+        $compute = function () use ($days): array {
+            return $this->computeSummitDaysWithEvents($days);
+        };
+
+        if ($lifetime <= 0) {
+            $with_events = $compute();
+        } else {
+            // the key carries the summit dates and timezone, so a stale list is never served after they change
+            $key = sprintf(
+                "summit_%s_dates_with_events_%s_%s_%s",
+                $this->id,
+                preg_replace('/[^A-Za-z0-9]/', '_', strval($this->getTimeZoneId())),
+                $this->begin_date->getTimestamp(),
+                $this->end_date->getTimestamp()
+            );
+            $with_events = Cache::remember($key, $lifetime, $compute);
+        }
+
+        return array_values(array_filter($days, function (DateTime $day) use ($with_events) {
+            return in_array($day->format('Y-m-d'), $with_events);
+        }));
+    }
+
+    /**
+     * Single query over the published events, the per day overlap test runs in PHP
+     * @param DateTime[] $days summit days (summit timezone)
+     * @return string[] Y-m-d of the days that have at least one published event
+     */
+    private function computeSummitDaysWithEvents(array $days): array
+    {
+        $sql = <<<SQL
+            SELECT SummitEvent.StartDate, SummitEvent.EndDate
             FROM SummitEvent
             WHERE
             SummitEvent.SummitID = :summit_id
             AND SummitEvent.Published = 1
-            AND (SummitEvent.StartDate <= :end and SummitEvent.EndDate >= :begin)
 SQL;
-                $stmt = $this->prepareRawSQL($sql, [
-                    'summit_id' => $this->id,
-                    'begin' => $begin->format("Y-m-d H:i:s"),
-                    'end' => $end->format('Y-m-d H:i:s'),
-                ]);
-                $res = $stmt->executeQuery();
-                $res = $res->fetchFirstColumn();
-                $count = count($res) > 0 ? $res[0] : 0;
-            } catch (\Exception $ex) {
-                Log::debug($ex);
-                $count = 0;
-            }
-            if ($count > 0) {
-                $list[] = $day;
+        $stmt = $this->prepareRawSQL($sql, ['summit_id' => $this->id]);
+        $events = $stmt->executeQuery()->fetchAllAssociative();
+
+        $list = [];
+        foreach ($days as $day) {
+            $begin = clone($day);
+            $begin = $begin->setTime(0, 0, 0)->setTimezone(new \DateTimeZone('UTC'))->format("Y-m-d H:i:s");
+            $end = clone($day);
+            $end = $end->setTime(23, 59, 59)->setTimezone(new \DateTimeZone('UTC'))->format("Y-m-d H:i:s");
+            foreach ($events as $event) {
+                // UTC "Y-m-d H:i:s" strings, same overlap test the SQL used to run
+                // a published event may lack dates, SQL never matched those rows (NULL comparison)
+                if (
+                    $event['StartDate'] !== null &&
+                    $event['EndDate'] !== null &&
+                    $event['StartDate'] <= $end &&
+                    $event['EndDate'] >= $begin
+                ) {
+                    $list[] = $day->format('Y-m-d');
+                    break;
+                }
             }
         }
-
         return $list;
     }
 
diff --git a/config/cache_api_response.php b/config/cache_api_response.php
index cb728400e..03be72541 100644
--- a/config/cache_api_response.php
+++ b/config/cache_api_response.php
@@ -20,4 +20,5 @@
     'get_summits_response_lifetime'         => env('CACHE_API_RESPONSE_GET_SUMMITS_LIFETIME', 600),
     'file_url_lifetime'                     => env('CACHE_API_RESPONSE_FILE_URL_LIFETIME', 3600),
     'event_has_access_lifetime'             => env('CACHE_API_RESPONSE_EVENT_HAS_ACCESS_LIFETIME', 600),
+    'summit_dates_with_events_lifetime'     => env('CACHE_API_RESPONSE_SUMMIT_DATES_WITH_EVENTS_LIFETIME', 300),
 ];
\ No newline at end of file
diff --git a/tests/SummitDaysWithEventsTest.php b/tests/SummitDaysWithEventsTest.php
new file mode 100644
index 000000000..a7d01692d
--- /dev/null
+++ b/tests/SummitDaysWithEventsTest.php
@@ -0,0 +1,142 @@
+<?php namespace Tests;
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Models\Foundation\Main\IGroup;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Config;
+use Illuminate\Support\Facades\DB;
+use models\summit\Summit;
+
+/**
+ * Summit::getSummitDaysWithEvents runs one query per summit and applies the per day
+ * overlap test in PHP, the result must match the former one COUNT per day implementation.
+ *
+ * Class SummitDaysWithEventsTest
+ */
+final class SummitDaysWithEventsTest extends TestCase
+{
+    use InsertSummitTestData;
+
+    use InsertMemberTestData;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        Config::set('cache_api_response.summit_dates_with_events_lifetime', 0);
+        self::insertMemberTestData(IGroup::TrackChairs);
+        self::$defaultMember = self::$member;
+        self::insertSummitTestData();
+    }
+
+    protected function tearDown(): void
+    {
+        self::clearSummitTestData();
+        self::clearMemberTestData();
+        parent::tearDown();
+    }
+
+    /**
+     * the former implementation, one COUNT per summit day
+     * @return string[]
+     */
+    private function legacyDaysWithEvents(Summit $summit): array
+    {
+        $res = [];
+        foreach ($summit->getSummitDays() as $day) {
+            $begin = (clone $day)->setTime(0, 0, 0)->setTimezone(new \DateTimeZone('UTC'));
+            $end = (clone $day)->setTime(23, 59, 59)->setTimezone(new \DateTimeZone('UTC'));
+            $count = DB::selectOne(
+                "SELECT COUNT(ID) AS QTY FROM SummitEvent WHERE SummitID = ? AND Published = 1 AND StartDate <= ? AND EndDate >= ?",
+                [$summit->getId(), $end->format('Y-m-d H:i:s'), $begin->format('Y-m-d H:i:s')]
+            )->QTY;
+            if ($count > 0) $res[] = $day->format('Y-m-d');
+        }
+        return $res;
+    }
+
+    private function daysWithEvents(Summit $summit): array
+    {
+        return array_map(function ($day) {
+            return $day->format('Y-m-d');
+        }, $summit->getSummitDaysWithEvents());
+    }
+
+    public function testMatchesPerDayImplementation(): void
+    {
+        $expected = $this->legacyDaysWithEvents(self::$summit);
+        $this->assertNotEmpty($expected);
+        $this->assertSame($expected, $this->daysWithEvents(self::$summit));
+    }
+
+    public function testEventCrossingDaysCountsOnBothDaysAndDaysWithoutEventsAreSkipped(): void
+    {
+        $summit_id = self::$summit->getId();
+        DB::update("UPDATE SummitEvent SET Published = 0 WHERE SummitID = ?", [$summit_id]);
+        $days = self::$summit->getSummitDays();
+
+        // one event from the evening of day 2 to the morning of day 3, summit timezone
+        $start = (clone $days[1])->setTime(22, 0, 0)->setTimezone(new \DateTimeZone('UTC'));
+        $end = (clone $days[2])->setTime(2, 0, 0)->setTimezone(new \DateTimeZone('UTC'));
+        $id = DB::selectOne("SELECT ID FROM SummitEvent WHERE SummitID = ? LIMIT 1", [$summit_id])->ID;
+        DB::update(
+            "UPDATE SummitEvent SET Published = 1, StartDate = ?, EndDate = ? WHERE ID = ?",
+            [$start->format('Y-m-d H:i:s'), $end->format('Y-m-d H:i:s'), $id]
+        );
+
+        $expected = [$days[1]->format('Y-m-d'), $days[2]->format('Y-m-d')];
+        $this->assertSame($expected, $this->daysWithEvents(self::$summit));
+        $this->assertSame($expected, $this->legacyDaysWithEvents(self::$summit));
+    }
+
+    public function testPublishedEventsWithoutDatesAreIgnored(): void
+    {
+        $summit_id = self::$summit->getId();
+        DB::update("UPDATE SummitEvent SET Published = 0 WHERE SummitID = ?", [$summit_id]);
+        $days = self::$summit->getSummitDays();
+        $end = (clone $days[2])->setTime(2, 0, 0)->setTimezone(new \DateTimeZone('UTC'));
+        $id = DB::selectOne("SELECT ID FROM SummitEvent WHERE SummitID = ? LIMIT 1", [$summit_id])->ID;
+        DB::update(
+            "UPDATE SummitEvent SET Published = 1, StartDate = NULL, EndDate = ? WHERE ID = ?",
+            [$end->format('Y-m-d H:i:s'), $id]
+        );
+
+        $this->assertSame([], $this->legacyDaysWithEvents(self::$summit));
+        $this->assertSame([], $this->daysWithEvents(self::$summit));
+    }
+
+    public function testRunsASingleSelectRegardlessOfTheNumberOfDays(): void
+    {
+        $this->assertGreaterThan(5, count(self::$summit->getSummitDays()));
+        $conn = self::$em->getConnection();
+        $selects = function () use ($conn): int {
+            return intval($conn->fetchAssociative("SHOW SESSION STATUS LIKE 'Com_select'")['Value']);
+        };
+        $before = $selects();
+        $this->daysWithEvents(self::$summit);
+        $this->assertSame(1, $selects() - $before);
+    }
+
+    public function testCachedListIsServedWithinTheLifetime(): void
+    {
+        Config::set('cache_api_response.summit_dates_with_events_lifetime', 300);
+        Cache::flush();
+        $first = $this->daysWithEvents(self::$summit);
+        $this->assertNotEmpty($first);
+        DB::update("UPDATE SummitEvent SET Published = 0 WHERE SummitID = ?", [self::$summit->getId()]);
+        $this->assertSame($first, $this->daysWithEvents(self::$summit));
+        Config::set('cache_api_response.summit_dates_with_events_lifetime', 0);
+        $this->assertSame([], $this->daysWithEvents(self::$summit));
+        Cache::flush();
+    }
+}