diff --git a/config/autoload/url-shortener.global.php b/config/autoload/url-shortener.global.php
index ec3c1409..2816577d 100644
--- a/config/autoload/url-shortener.global.php
+++ b/config/autoload/url-shortener.global.php
@@ -3,6 +3,7 @@
 declare(strict_types=1);
 
 use Shlinkio\Shlink\Core\Config\EnvVars;
+use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlMode;
 
 use const Shlinkio\Shlink\DEFAULT_SHORT_CODES_LENGTH;
 use const Shlinkio\Shlink\MIN_SHORT_CODES_LENGTH;
@@ -12,6 +13,8 @@ return (static function (): array {
         (int) EnvVars::DEFAULT_SHORT_CODES_LENGTH->loadFromEnv(DEFAULT_SHORT_CODES_LENGTH),
         MIN_SHORT_CODES_LENGTH,
     );
+    $modeFromEnv = EnvVars::SHORT_URL_MODE->loadFromEnv(ShortUrlMode::STRICT->value);
+    $mode = ShortUrlMode::tryFrom($modeFromEnv) ?? ShortUrlMode::STRICT;
 
     return [
 
@@ -25,6 +28,7 @@ return (static function (): array {
             'append_extra_path' => (bool) EnvVars::REDIRECT_APPEND_EXTRA_PATH->loadFromEnv(false),
             'multi_segment_slugs_enabled' => (bool) EnvVars::MULTI_SEGMENT_SLUGS_ENABLED->loadFromEnv(false),
             'trailing_slash_enabled' => (bool) EnvVars::SHORT_URL_TRAILING_SLASH->loadFromEnv(false),
+            'mode' => $mode,
         ],
 
     ];
diff --git a/module/CLI/src/Command/ShortUrl/CreateShortUrlCommand.php b/module/CLI/src/Command/ShortUrl/CreateShortUrlCommand.php
index 71ab5fa7..46a1cc8f 100644
--- a/module/CLI/src/Command/ShortUrl/CreateShortUrlCommand.php
+++ b/module/CLI/src/Command/ShortUrl/CreateShortUrlCommand.php
@@ -176,7 +176,7 @@ class CreateShortUrlCommand extends Command
                 ShortUrlInputFilter::CRAWLABLE => $input->getOption('crawlable'),
                 ShortUrlInputFilter::FORWARD_QUERY => !$input->getOption('no-forward-query'),
                 EnvVars::MULTI_SEGMENT_SLUGS_ENABLED->value => $this->options->multiSegmentSlugsEnabled,
-            ]));
+            ], $this->options->mode));
 
             $io->writeln([
                 sprintf('Processed long URL: <info>%s</info>', $longUrl),
diff --git a/module/Core/config/dependencies.config.php b/module/Core/config/dependencies.config.php
index 48fe3cb2..40985f42 100644
--- a/module/Core/config/dependencies.config.php
+++ b/module/Core/config/dependencies.config.php
@@ -137,7 +137,7 @@ return [
             ShortUrl\ShortUrlResolver::class,
         ],
         ShortUrl\ShortUrlResolver::class => ['em'],
-        ShortUrl\Helper\ShortCodeUniquenessHelper::class => ['em'],
+        ShortUrl\Helper\ShortCodeUniquenessHelper::class => ['em', Options\UrlShortenerOptions::class],
         Domain\DomainService::class => ['em', 'config.url_shortener.domain.hostname'],
 
         Util\UrlValidator::class => ['httpClient', Options\UrlShortenerOptions::class],
diff --git a/module/Core/functions/functions.php b/module/Core/functions/functions.php
index 574d604c..b6acbb35 100644
--- a/module/Core/functions/functions.php
+++ b/module/Core/functions/functions.php
@@ -15,6 +15,7 @@ use Laminas\Filter\Word\CamelCaseToUnderscore;
 use Laminas\InputFilter\InputFilter;
 use PUGX\Shortid\Factory as ShortIdFactory;
 use Shlinkio\Shlink\Common\Util\DateRange;
+use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlMode;
 
 use function date_default_timezone_get;
 use function Functional\map;
@@ -27,14 +28,16 @@ use function str_repeat;
 use function strtolower;
 use function ucfirst;
 
-function generateRandomShortCode(int $length): string
+function generateRandomShortCode(int $length, ShortUrlMode $mode = ShortUrlMode::STRICT): string
 {
     static $shortIdFactory;
     if ($shortIdFactory === null) {
         $shortIdFactory = new ShortIdFactory();
     }
 
-    $alphabet = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
+    $alphabet = $mode === ShortUrlMode::STRICT
+        ? '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+        : '0123456789abcdefghijklmnopqrstuvwxyz';
     return $shortIdFactory->generate($length, $alphabet)->serialize();
 }
 
diff --git a/module/Core/src/Config/EnvVars.php b/module/Core/src/Config/EnvVars.php
index 75454ecc..44919415 100644
--- a/module/Core/src/Config/EnvVars.php
+++ b/module/Core/src/Config/EnvVars.php
@@ -43,6 +43,7 @@ enum EnvVars: string
     case REDIRECT_CACHE_LIFETIME = 'REDIRECT_CACHE_LIFETIME';
     case BASE_PATH = 'BASE_PATH';
     case SHORT_URL_TRAILING_SLASH = 'SHORT_URL_TRAILING_SLASH';
+    case SHORT_URL_MODE = 'SHORT_URL_MODE';
     case PORT = 'PORT';
     case TASK_WORKER_NUM = 'TASK_WORKER_NUM';
     case WEB_WORKER_NUM = 'WEB_WORKER_NUM';
diff --git a/module/Core/src/Options/UrlShortenerOptions.php b/module/Core/src/Options/UrlShortenerOptions.php
index 9aacc085..827988fa 100644
--- a/module/Core/src/Options/UrlShortenerOptions.php
+++ b/module/Core/src/Options/UrlShortenerOptions.php
@@ -4,6 +4,8 @@ declare(strict_types=1);
 
 namespace Shlinkio\Shlink\Core\Options;
 
+use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlMode;
+
 use const Shlinkio\Shlink\DEFAULT_SHORT_CODES_LENGTH;
 
 final class UrlShortenerOptions
@@ -16,6 +18,7 @@ final class UrlShortenerOptions
         public readonly bool $appendExtraPath = false,
         public readonly bool $multiSegmentSlugsEnabled = false,
         public readonly bool $trailingSlashEnabled = false,
+        public readonly ShortUrlMode $mode = ShortUrlMode::STRICT,
     ) {
     }
 }
diff --git a/module/Core/src/ShortUrl/Entity/ShortUrl.php b/module/Core/src/ShortUrl/Entity/ShortUrl.php
index d0e9cba4..e3d6544c 100644
--- a/module/Core/src/ShortUrl/Entity/ShortUrl.php
+++ b/module/Core/src/ShortUrl/Entity/ShortUrl.php
@@ -16,6 +16,7 @@ use Shlinkio\Shlink\Core\Model\DeviceType;
 use Shlinkio\Shlink\Core\ShortUrl\Model\DeviceLongUrlPair;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlCreation;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlEdition;
+use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlMode;
 use Shlinkio\Shlink\Core\ShortUrl\Model\Validation\ShortUrlInputFilter;
 use Shlinkio\Shlink\Core\ShortUrl\Resolver\ShortUrlRelationResolverInterface;
 use Shlinkio\Shlink\Core\ShortUrl\Resolver\SimpleShortUrlRelationResolver;
@@ -95,7 +96,10 @@ class ShortUrl extends AbstractEntity
         $instance->maxVisits = $creation->maxVisits;
         $instance->customSlugWasProvided = $creation->hasCustomSlug();
         $instance->shortCodeLength = $creation->shortCodeLength;
-        $instance->shortCode = $creation->customSlug ?? generateRandomShortCode($instance->shortCodeLength);
+        $instance->shortCode = $creation->customSlug ?? generateRandomShortCode(
+            $instance->shortCodeLength,
+            $creation->shortUrlMode,
+        );
         $instance->domain = $relationResolver->resolveDomain($creation->domain);
         $instance->authorApiKey = $creation->apiKey;
         $instance->title = $creation->title;
@@ -292,7 +296,7 @@ class ShortUrl extends AbstractEntity
     /**
      * @throws ShortCodeCannotBeRegeneratedException
      */
-    public function regenerateShortCode(): void
+    public function regenerateShortCode(ShortUrlMode $mode): void
     {
         // In ShortUrls where a custom slug was provided, throw error, unless it is an imported one
         if ($this->customSlugWasProvided && $this->importSource === null) {
@@ -304,7 +308,7 @@ class ShortUrl extends AbstractEntity
             throw ShortCodeCannotBeRegeneratedException::forShortUrlAlreadyPersisted();
         }
 
-        $this->shortCode = generateRandomShortCode($this->shortCodeLength);
+        $this->shortCode = generateRandomShortCode($this->shortCodeLength, $mode);
     }
 
     public function isEnabled(): bool
diff --git a/module/Core/src/ShortUrl/Helper/ShortCodeUniquenessHelper.php b/module/Core/src/ShortUrl/Helper/ShortCodeUniquenessHelper.php
index 1f16f037..b428019e 100644
--- a/module/Core/src/ShortUrl/Helper/ShortCodeUniquenessHelper.php
+++ b/module/Core/src/ShortUrl/Helper/ShortCodeUniquenessHelper.php
@@ -5,14 +5,17 @@ declare(strict_types=1);
 namespace Shlinkio\Shlink\Core\ShortUrl\Helper;
 
 use Doctrine\ORM\EntityManagerInterface;
+use Shlinkio\Shlink\Core\Options\UrlShortenerOptions;
 use Shlinkio\Shlink\Core\ShortUrl\Entity\ShortUrl;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlIdentifier;
 use Shlinkio\Shlink\Core\ShortUrl\Repository\ShortUrlRepository;
 
 class ShortCodeUniquenessHelper implements ShortCodeUniquenessHelperInterface
 {
-    public function __construct(private readonly EntityManagerInterface $em)
-    {
+    public function __construct(
+        private readonly EntityManagerInterface $em,
+        private readonly UrlShortenerOptions $options,
+    ) {
     }
 
     public function ensureShortCodeUniqueness(ShortUrl $shortUrlToBeCreated, bool $hasCustomSlug): bool
@@ -29,7 +32,7 @@ class ShortCodeUniquenessHelper implements ShortCodeUniquenessHelperInterface
             return false;
         }
 
-        $shortUrlToBeCreated->regenerateShortCode();
+        $shortUrlToBeCreated->regenerateShortCode($this->options->mode);
         return $this->ensureShortCodeUniqueness($shortUrlToBeCreated, $hasCustomSlug);
     }
 }
diff --git a/module/Core/src/ShortUrl/Model/ShortUrlCreation.php b/module/Core/src/ShortUrl/Model/ShortUrlCreation.php
index c29817b6..d0d9b279 100644
--- a/module/Core/src/ShortUrl/Model/ShortUrlCreation.php
+++ b/module/Core/src/ShortUrl/Model/ShortUrlCreation.php
@@ -25,6 +25,7 @@ final class ShortUrlCreation implements TitleResolutionModelInterface
      */
     private function __construct(
         public readonly string $longUrl,
+        public readonly ShortUrlMode $shortUrlMode,
         public readonly array $deviceLongUrls = [],
         public readonly ?Chronos $validSince = null,
         public readonly ?Chronos $validUntil = null,
@@ -47,7 +48,7 @@ final class ShortUrlCreation implements TitleResolutionModelInterface
     /**
      * @throws ValidationException
      */
-    public static function fromRawData(array $data): self
+    public static function fromRawData(array $data, ShortUrlMode $mode = ShortUrlMode::STRICT): self
     {
         $inputFilter = ShortUrlInputFilter::withRequiredLongUrl($data);
         if (! $inputFilter->isValid()) {
@@ -60,6 +61,7 @@ final class ShortUrlCreation implements TitleResolutionModelInterface
 
         return new self(
             longUrl: $inputFilter->getValue(ShortUrlInputFilter::LONG_URL),
+            shortUrlMode: $mode,
             deviceLongUrls: $deviceLongUrls,
             validSince: normalizeOptionalDate($inputFilter->getValue(ShortUrlInputFilter::VALID_SINCE)),
             validUntil: normalizeOptionalDate($inputFilter->getValue(ShortUrlInputFilter::VALID_UNTIL)),
@@ -84,6 +86,7 @@ final class ShortUrlCreation implements TitleResolutionModelInterface
     {
         return new self(
             longUrl: $this->longUrl,
+            shortUrlMode: $this->shortUrlMode,
             deviceLongUrls: $this->deviceLongUrls,
             validSince: $this->validSince,
             validUntil: $this->validUntil,
diff --git a/module/Core/src/ShortUrl/Model/ShortUrlMode.php b/module/Core/src/ShortUrl/Model/ShortUrlMode.php
new file mode 100644
index 00000000..41698e18
--- /dev/null
+++ b/module/Core/src/ShortUrl/Model/ShortUrlMode.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace Shlinkio\Shlink\Core\ShortUrl\Model;
+
+enum ShortUrlMode: string
+{
+    case STRICT = 'strict';
+    case LOOSELY = 'loosely';
+}
diff --git a/module/Core/src/ShortUrl/Model/Validation/ShortUrlInputFilter.php b/module/Core/src/ShortUrl/Model/Validation/ShortUrlInputFilter.php
index 68b87158..020cdfd2 100644
--- a/module/Core/src/ShortUrl/Model/Validation/ShortUrlInputFilter.php
+++ b/module/Core/src/ShortUrl/Model/Validation/ShortUrlInputFilter.php
@@ -42,7 +42,6 @@ class ShortUrlInputFilter extends InputFilter
 
     private function __construct(array $data, bool $requireLongUrl)
     {
-        // FIXME The multi-segment slug option should be injected
         $this->initialize($requireLongUrl, $data[EnvVars::MULTI_SEGMENT_SLUGS_ENABLED->value] ?? false);
         $this->setData($data);
     }
diff --git a/module/Core/test/ShortUrl/Entity/ShortUrlTest.php b/module/Core/test/ShortUrl/Entity/ShortUrlTest.php
index 2d950d5f..be1747fd 100644
--- a/module/Core/test/ShortUrl/Entity/ShortUrlTest.php
+++ b/module/Core/test/ShortUrl/Entity/ShortUrlTest.php
@@ -11,13 +11,16 @@ use Shlinkio\Shlink\Core\Model\DeviceType;
 use Shlinkio\Shlink\Core\ShortUrl\Entity\ShortUrl;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlCreation;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlEdition;
+use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlMode;
 use Shlinkio\Shlink\Core\ShortUrl\Model\Validation\ShortUrlInputFilter;
 use Shlinkio\Shlink\Importer\Model\ImportedShlinkUrl;
 use Shlinkio\Shlink\Importer\Sources\ImportSource;
 
+use function Functional\every;
 use function Functional\map;
 use function range;
 use function strlen;
+use function strtolower;
 
 use const Shlinkio\Shlink\DEFAULT_SHORT_CODES_LENGTH;
 
@@ -34,7 +37,7 @@ class ShortUrlTest extends TestCase
         $this->expectException(ShortCodeCannotBeRegeneratedException::class);
         $this->expectExceptionMessage($expectedMessage);
 
-        $shortUrl->regenerateShortCode();
+        $shortUrl->regenerateShortCode(ShortUrlMode::STRICT);
     }
 
     public function provideInvalidShortUrls(): iterable
@@ -58,7 +61,7 @@ class ShortUrlTest extends TestCase
     ): void {
         $firstShortCode = $shortUrl->getShortCode();
 
-        $shortUrl->regenerateShortCode();
+        $shortUrl->regenerateShortCode(ShortUrlMode::STRICT);
         $secondShortCode = $shortUrl->getShortCode();
 
         self::assertNotEquals($firstShortCode, $secondShortCode);
@@ -133,4 +136,22 @@ class ShortUrlTest extends TestCase
             DeviceType::DESKTOP->value => 'desktop',
         ], $shortUrl->deviceLongUrls());
     }
+
+    /** @test */
+    public function generatesLowercaseOnlyShortCodesInLooselyMode(): void
+    {
+        $range = range(1, 1000); // Use a "big" number to reduce false negatives
+        $allFor = static fn (ShortUrlMode $mode): bool => every($range, static function () use ($mode): bool {
+            $shortUrl = ShortUrl::create(ShortUrlCreation::fromRawData(
+                [ShortUrlInputFilter::LONG_URL => 'foo'],
+                $mode,
+            ));
+            $shortCode = $shortUrl->getShortCode();
+
+            return $shortCode === strtolower($shortCode);
+        });
+
+        self::assertTrue($allFor(ShortUrlMode::LOOSELY));
+        self::assertFalse($allFor(ShortUrlMode::STRICT));
+    }
 }
diff --git a/module/Core/test/ShortUrl/Helper/ShortCodeUniquenessHelperTest.php b/module/Core/test/ShortUrl/Helper/ShortCodeUniquenessHelperTest.php
index 5df79fc5..ae0d9363 100644
--- a/module/Core/test/ShortUrl/Helper/ShortCodeUniquenessHelperTest.php
+++ b/module/Core/test/ShortUrl/Helper/ShortCodeUniquenessHelperTest.php
@@ -8,6 +8,7 @@ use Doctrine\ORM\EntityManagerInterface;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 use Shlinkio\Shlink\Core\Domain\Entity\Domain;
+use Shlinkio\Shlink\Core\Options\UrlShortenerOptions;
 use Shlinkio\Shlink\Core\ShortUrl\Entity\ShortUrl;
 use Shlinkio\Shlink\Core\ShortUrl\Helper\ShortCodeUniquenessHelper;
 use Shlinkio\Shlink\Core\ShortUrl\Model\ShortUrlIdentifier;
@@ -22,7 +23,7 @@ class ShortCodeUniquenessHelperTest extends TestCase
     protected function setUp(): void
     {
         $this->em = $this->createMock(EntityManagerInterface::class);
-        $this->helper = new ShortCodeUniquenessHelper($this->em);
+        $this->helper = new ShortCodeUniquenessHelper($this->em, new UrlShortenerOptions());
 
         $this->shortUrl = $this->createMock(ShortUrl::class);
         $this->shortUrl->method('getShortCode')->willReturn('abc123');
diff --git a/module/Rest/src/Action/ShortUrl/CreateShortUrlAction.php b/module/Rest/src/Action/ShortUrl/CreateShortUrlAction.php
index e60414b2..c7b6b33f 100644
--- a/module/Rest/src/Action/ShortUrl/CreateShortUrlAction.php
+++ b/module/Rest/src/Action/ShortUrl/CreateShortUrlAction.php
@@ -25,6 +25,6 @@ class CreateShortUrlAction extends AbstractCreateShortUrlAction
         $payload[ShortUrlInputFilter::API_KEY] = AuthenticationMiddleware::apiKeyFromRequest($request);
         $payload[EnvVars::MULTI_SEGMENT_SLUGS_ENABLED->value] = $this->urlShortenerOptions->multiSegmentSlugsEnabled;
 
-        return ShortUrlCreation::fromRawData($payload);
+        return ShortUrlCreation::fromRawData($payload, $this->urlShortenerOptions->mode);
     }
 }
diff --git a/module/Rest/src/Action/ShortUrl/SingleStepCreateShortUrlAction.php b/module/Rest/src/Action/ShortUrl/SingleStepCreateShortUrlAction.php
index 89989dda..b32e8a5d 100644
--- a/module/Rest/src/Action/ShortUrl/SingleStepCreateShortUrlAction.php
+++ b/module/Rest/src/Action/ShortUrl/SingleStepCreateShortUrlAction.php
@@ -25,6 +25,6 @@ class SingleStepCreateShortUrlAction extends AbstractCreateShortUrlAction
             ShortUrlInputFilter::API_KEY => $apiKey,
             // This will usually be null, unless this API key enforces one specific domain
             ShortUrlInputFilter::DOMAIN => $request->getAttribute(ShortUrlInputFilter::DOMAIN),
-        ]);
+        ], $this->urlShortenerOptions->mode);
     }
 }