diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index eecf859d2..50da29b7c 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -19,13 +19,8 @@ jobs:
             fail-fast: false
             matrix:
                 include:
-                  - php: '7.1'
-                  - php: '7.2'
-                  - php: '7.3'
-                  - php: '7.4'
                   - php: '8.0'
                   - php: '8.1'
-                  - php: '7.4'
                     mode: low-deps
 
         steps:
@@ -42,9 +37,8 @@ jobs:
             - name: "Validate composer.json"
               run: "composer validate --strict --no-check-lock"
 
-            - run: |
-                composer require --no-update composer/composer:^1.0.2 --ansi
-
+            - name: "Install dependencies"
+              run: |
                 if [[ "${{ matrix.mode }}" = low-deps ]]; then
                     composer u --prefer-lowest --prefer-stable --ansi
                 else
@@ -56,17 +50,6 @@ jobs:
 
             - run: vendor/bin/simple-phpunit
 
-            - run: |
-                composer require --no-update composer/composer:^2 --ansi
-
-                if [[ "${{ matrix.mode }}" = low-deps ]]; then
-                    composer u --prefer-lowest --prefer-stable --ansi
-                else
-                    composer u --ansi
-                fi
-
-            - run: vendor/bin/simple-phpunit
-
-            - if: matrix.php == '7.1'
+            - if: matrix.php == '8.0'
               name: "Lint PHP files"
               run: find src/ -name '*.php' | xargs -n1 php -l
diff --git a/composer.json b/composer.json
index 0e1e7c3b2..fc229bac3 100644
--- a/composer.json
+++ b/composer.json
@@ -11,25 +11,28 @@
     ],
     "minimum-stability": "dev",
     "require": {
-        "php": ">=7.1",
-        "composer-plugin-api": "^1.0|^2.0"
+        "php": ">=8.0",
+        "composer-plugin-api": "^2.1"
     },
     "require-dev": {
-        "composer/composer": "^1.0.2|^2.0",
-        "symfony/dotenv": "^4.4|^5.0|^6.0",
-        "symfony/filesystem": "^4.4|^5.0|^6.0",
-        "symfony/phpunit-bridge": "^4.4.12|^5.0|^6.0",
-        "symfony/process": "^4.4|^5.0|^6.0"
+        "composer/composer": "^2.1",
+        "symfony/dotenv": "^5.4|^6.0",
+        "symfony/filesystem": "^5.4|^6.0",
+        "symfony/phpunit-bridge": "^5.4|^6.0",
+        "symfony/process": "^5.4|^6.0"
     },
     "autoload": {
         "psr-4": {
             "Symfony\\Flex\\": "src"
         }
     },
+    "replace": {
+        "symfony/polyfill-php72": "*",
+        "symfony/polyfill-php73": "*",
+        "symfony/polyfill-php74": "*",
+        "symfony/polyfill-php80": "*"
+    },
     "extra": {
-        "branch-alias": {
-            "dev-main": "1.17-dev"
-        },
         "class": "Symfony\\Flex\\Flex"
     }
 }
diff --git a/src/Cache.php b/src/Cache.php
deleted file mode 100644
index d1c00248d..000000000
--- a/src/Cache.php
+++ /dev/null
@@ -1,158 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex;
-
-use Composer\Cache as BaseCache;
-use Composer\IO\IOInterface;
-use Composer\Package\RootPackageInterface;
-use Composer\Semver\Constraint\Constraint;
-use Composer\Semver\VersionParser;
-
-/**
- * @author Nicolas Grekas <p@tchwork.com>
- */
-class Cache extends BaseCache
-{
-    private $versions;
-    private $versionParser;
-    private $symfonyRequire;
-    private $rootConstraints = [];
-    private $symfonyConstraints;
-    private $downloader;
-    private $io;
-
-    public function setSymfonyRequire(string $symfonyRequire, RootPackageInterface $rootPackage, Downloader $downloader, IOInterface $io = null)
-    {
-        $this->versionParser = new VersionParser();
-        $this->symfonyRequire = $symfonyRequire;
-        $this->symfonyConstraints = $this->versionParser->parseConstraints($symfonyRequire);
-        $this->downloader = $downloader;
-        $this->io = $io;
-
-        foreach ($rootPackage->getRequires() + $rootPackage->getDevRequires() as $name => $link) {
-            $this->rootConstraints[$name] = $link->getConstraint();
-        }
-    }
-
-    public function read($file)
-    {
-        $content = parent::read($file);
-
-        if (0 === strpos($file, 'provider-symfony$') && \is_array($data = json_decode($content, true))) {
-            $content = json_encode($this->removeLegacyTags($data));
-        }
-
-        return $content;
-    }
-
-    public function removeLegacyTags(array $data): array
-    {
-        if (!$this->symfonyConstraints || !isset($data['packages'])) {
-            return $data;
-        }
-
-        foreach ($data['packages'] as $name => $versions) {
-            if (!isset($this->getVersions()['splits'][$name])) {
-                continue;
-            }
-
-            $rootConstraint = $this->rootConstraints[$name] ?? null;
-            $rootVersions = [];
-
-            foreach ($versions as $version => $composerJson) {
-                if (null !== $alias = $composerJson['extra']['branch-alias'][$version] ?? null) {
-                    $normalizedVersion = $this->versionParser->normalize($alias);
-                } elseif (null === $normalizedVersion = $composerJson['version_normalized'] ?? null) {
-                    continue;
-                }
-
-                $constraint = new Constraint('==', $normalizedVersion);
-
-                if ($rootConstraint && $rootConstraint->matches($constraint)) {
-                    $rootVersions[$version] = $composerJson;
-                }
-
-                if (!$this->symfonyConstraints->matches($constraint)) {
-                    if (null !== $this->io) {
-                        $this->io->writeError(sprintf('<info>Restricting packages listed in "symfony/symfony" to "%s"</>', $this->symfonyRequire));
-                        $this->io = null;
-                    }
-                    unset($versions[$version]);
-                }
-            }
-
-            if ($rootConstraint && !array_intersect_key($rootVersions, $versions)) {
-                $versions = $rootVersions;
-            }
-
-            $data['packages'][$name] = $versions;
-        }
-
-        if (null === $symfonySymfony = $data['packages']['symfony/symfony'] ?? null) {
-            return $data;
-        }
-
-        foreach ($symfonySymfony as $version => $composerJson) {
-            if (null !== $alias = $composerJson['extra']['branch-alias'][$version] ?? null) {
-                $normalizedVersion = $this->versionParser->normalize($alias);
-            } elseif (null === $normalizedVersion = $composerJson['version_normalized'] ?? null) {
-                continue;
-            }
-
-            if (!$this->symfonyConstraints->matches(new Constraint('==', $normalizedVersion))) {
-                unset($symfonySymfony[$version]);
-            }
-        }
-
-        if ($symfonySymfony) {
-            $data['packages']['symfony/symfony'] = $symfonySymfony;
-        }
-
-        return $data;
-    }
-
-    private function getVersions(): array
-    {
-        if (null !== $this->versions) {
-            return $this->versions;
-        }
-
-        $versions = $this->downloader->getVersions();
-        $this->downloader = null;
-        $okVersions = [];
-
-        foreach ($versions['splits'] as $name => $vers) {
-            foreach ($vers as $i => $v) {
-                if (!isset($okVersions[$v])) {
-                    $okVersions[$v] = false;
-
-                    for ($j = 0; $j < 60; ++$j) {
-                        if ($this->symfonyConstraints->matches(new Constraint('==', $v.'.'.$j.'.0'))) {
-                            $okVersions[$v] = true;
-                            break;
-                        }
-                    }
-                }
-
-                if (!$okVersions[$v]) {
-                    unset($vers[$i]);
-                }
-            }
-
-            if (!$vers || $vers === $versions['splits'][$name]) {
-                unset($versions['splits'][$name]);
-            }
-        }
-
-        return $this->versions = $versions;
-    }
-}
diff --git a/src/Command/GenerateIdCommand.php b/src/Command/GenerateIdCommand.php
deleted file mode 100644
index f26261587..000000000
--- a/src/Command/GenerateIdCommand.php
+++ /dev/null
@@ -1,39 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex\Command;
-
-use Symfony\Component\Console\Command\Command;
-use Symfony\Component\Console\Input\InputInterface;
-use Symfony\Component\Console\Output\OutputInterface;
-use Symfony\Component\Console\Style\SymfonyStyle;
-
-class GenerateIdCommand extends Command
-{
-    public function __construct()
-    {
-        // No-op to support downgrading to v1.12.x
-        parent::__construct();
-    }
-
-    protected function configure()
-    {
-        $this->setName('symfony:generate-id');
-    }
-
-    protected function execute(InputInterface $input, OutputInterface $output): int
-    {
-        $ui = new SymfonyStyle($input, $output);
-        $ui->error('This command is a noop and should not be used anymore.');
-
-        return 1;
-    }
-}
diff --git a/src/Command/RecipesCommand.php b/src/Command/RecipesCommand.php
index 1d65648c7..2820d7730 100644
--- a/src/Command/RecipesCommand.php
+++ b/src/Command/RecipesCommand.php
@@ -30,10 +30,10 @@ class RecipesCommand extends BaseCommand
     /** @var \Symfony\Flex\Flex */
     private $flex;
 
-    private $symfonyLock;
-    private $downloader;
+    private Lock $symfonyLock;
+    private HttpDownloader $downloader;
 
-    public function __construct(/* cannot be type-hinted */ $flex, Lock $symfonyLock, $downloader)
+    public function __construct(/* cannot be type-hinted */ $flex, Lock $symfonyLock, HttpDownloader $downloader)
     {
         $this->flex = $flex;
         $this->symfonyLock = $symfonyLock;
@@ -102,7 +102,6 @@ protected function execute(InputInterface $input, OutputInterface $output)
 
         $write = [];
         $hasOutdatedRecipes = false;
-        /** @var Recipe $recipe */
         foreach ($recipes as $name => $recipe) {
             $lockRef = $this->symfonyLock->get($name)['recipe']['ref'] ?? null;
 
@@ -375,11 +374,7 @@ private function findRecipeCommitDataFromTreeRef(string $package, string $repo,
 
     private function requestGitHubApi(string $path)
     {
-        if ($this->downloader instanceof HttpDownloader) {
-            $contents = $this->downloader->get($path)->getBody();
-        } else {
-            $contents = $this->downloader->getContents('api.github.com', $path, false);
-        }
+        $contents = $this->downloader->get($path)->getBody();
 
         return json_decode($contents, true);
     }
diff --git a/src/Command/RequireCommand.php b/src/Command/RequireCommand.php
index a92eef093..faa76c5b4 100644
--- a/src/Command/RequireCommand.php
+++ b/src/Command/RequireCommand.php
@@ -15,7 +15,6 @@
 use Composer\Factory;
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
-use Composer\Plugin\PluginInterface;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Output\OutputInterface;
@@ -56,10 +55,6 @@ protected function execute(InputInterface $input, OutputInterface $output)
             $input->setArgument('packages', $this->resolver->resolve($input->getArgument('packages'), true));
         }
 
-        if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>') && $input->hasOption('no-suggest')) {
-            $input->setOption('no-suggest', true);
-        }
-
         $file = Factory::getComposerFile();
         $contents = file_get_contents($file);
         $json = JsonFile::parseJson($contents);
diff --git a/src/Command/UnpackCommand.php b/src/Command/UnpackCommand.php
deleted file mode 100644
index 3f62108e3..000000000
--- a/src/Command/UnpackCommand.php
+++ /dev/null
@@ -1,128 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex\Command;
-
-use Composer\Command\BaseCommand;
-use Composer\Factory;
-use Composer\Installer;
-use Composer\Package\Version\VersionParser;
-use Symfony\Component\Console\Input\InputArgument;
-use Symfony\Component\Console\Input\InputInterface;
-use Symfony\Component\Console\Input\InputOption;
-use Symfony\Component\Console\Output\OutputInterface;
-use Symfony\Flex\PackageResolver;
-use Symfony\Flex\Unpack\Operation;
-use Symfony\Flex\Unpacker;
-
-/**
- * @deprecated since Flex 1.4
- */
-class UnpackCommand extends BaseCommand
-{
-    private $resolver;
-
-    public function __construct(PackageResolver $resolver)
-    {
-        $this->resolver = $resolver;
-
-        parent::__construct();
-    }
-
-    protected function configure()
-    {
-        $this->setName('symfony:unpack')
-            ->setAliases(['unpack'])
-            ->setDescription('[DEPRECATED] Unpacks a Symfony pack.')
-            ->setDefinition([
-                new InputArgument('packages', InputArgument::IS_ARRAY | InputArgument::REQUIRED, 'Installed packages to unpack.'),
-                new InputOption('sort-packages', null, InputOption::VALUE_NONE, 'Sorts packages'),
-            ])
-        ;
-    }
-
-    protected function execute(InputInterface $input, OutputInterface $output)
-    {
-        $composer = $this->getComposer();
-        $packages = $this->resolver->resolve($input->getArgument('packages'), true);
-        $io = $this->getIO();
-        $lockData = $composer->getLocker()->getLockData();
-        $installedRepo = $composer->getRepositoryManager()->getLocalRepository();
-        $versionParser = new VersionParser();
-        $dryRun = $input->hasOption('dry-run') && $input->getOption('dry-run');
-
-        $io->writeError('<warning>Command "symfony:unpack" is deprecated, Symfony packs are always unpacked now.</>');
-
-        $op = new Operation(true, $input->getOption('sort-packages') || $composer->getConfig()->get('sort-packages'));
-        foreach ($versionParser->parseNameVersionPairs($packages) as $package) {
-            if (null === $pkg = $installedRepo->findPackage($package['name'], '*')) {
-                $io->writeError(sprintf('<error>Package %s is not installed</>', $package['name']));
-
-                return 1;
-            }
-
-            $dev = false;
-            foreach ($lockData['packages-dev'] as $p) {
-                if ($package['name'] === $p['name']) {
-                    $dev = true;
-
-                    break;
-                }
-            }
-
-            $op->addPackage($pkg->getName(), $pkg->getVersion(), $dev);
-        }
-
-        $unpacker = new Unpacker($composer, $this->resolver, $dryRun);
-        $result = $unpacker->unpack($op);
-
-        // remove the packages themselves
-        if (!$result->getUnpacked()) {
-            $io->writeError('<info>Nothing to unpack</>');
-
-            return 0;
-        }
-
-        $io->writeError('<info>Unpacking Symfony packs</>');
-        foreach ($result->getUnpacked() as $pkg) {
-            $io->writeError(sprintf('  - Unpacked <info>%s</>', $pkg->getName()));
-        }
-
-        $unpacker->updateLock($result, $io);
-
-        if ($input->hasOption('no-install') && $input->getOption('no-install')) {
-            return 0;
-        }
-
-        $composer = Factory::create($io, null, true);
-        $installer = Installer::create($io, $composer);
-        $installer
-            ->setDryRun($dryRun)
-            ->setDevMode(true)
-            ->setDumpAutoloader(false)
-            ->setIgnorePlatformRequirements(true)
-            ->setUpdate(true)
-            ->setUpdateAllowList(['php'])
-        ;
-
-        if (method_exists($composer->getEventDispatcher(), 'setRunScripts')) {
-            $composer->getEventDispatcher()->setRunScripts(false);
-        } else {
-            $installer->setRunScripts(false);
-        }
-
-        if (method_exists($installer, 'setSkipSuggest')) {
-            $installer->setSkipSuggest(true);
-        }
-
-        return $installer->run();
-    }
-}
diff --git a/src/Command/UpdateCommand.php b/src/Command/UpdateCommand.php
index 82329f4df..364b772eb 100644
--- a/src/Command/UpdateCommand.php
+++ b/src/Command/UpdateCommand.php
@@ -12,7 +12,6 @@
 namespace Symfony\Flex\Command;
 
 use Composer\Command\UpdateCommand as BaseUpdateCommand;
-use Composer\Plugin\PluginInterface;
 use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Flex\PackageResolver;
@@ -32,10 +31,6 @@ protected function execute(InputInterface $input, OutputInterface $output)
     {
         $input->setArgument('packages', $this->resolver->resolve($input->getArgument('packages')));
 
-        if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>') && $input->hasOption('no-suggest')) {
-            $input->setOption('no-suggest', true);
-        }
-
         return parent::execute($input, $output);
     }
 }
diff --git a/src/ComposerRepository.php b/src/ComposerRepository.php
deleted file mode 100644
index 26bbb16be..000000000
--- a/src/ComposerRepository.php
+++ /dev/null
@@ -1,58 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex;
-
-use Composer\Repository\ComposerRepository as BaseComposerRepository;
-
-/**
- * @author Nicolas Grekas <p@tchwork.com>
- */
-class ComposerRepository extends BaseComposerRepository
-{
-    private $providerFiles;
-
-    protected function loadProviderListings($data)
-    {
-        if (null !== $this->providerFiles) {
-            parent::loadProviderListings($data);
-
-            return;
-        }
-
-        $data = [$data];
-
-        while ($data) {
-            $this->providerFiles = [];
-            foreach ($data as $data) {
-                $this->loadProviderListings($data);
-            }
-
-            $loadingFiles = $this->providerFiles;
-            $this->providerFiles = null;
-            $data = [];
-            $this->rfs->download($loadingFiles, function (...$args) use (&$data) {
-                $data[] = $this->fetchFile(...$args);
-            });
-        }
-    }
-
-    protected function fetchFile($filename, $cacheKey = null, $sha256 = null, $storeLastModifiedTime = false)
-    {
-        if (null !== $this->providerFiles) {
-            $this->providerFiles[] = [$filename, $cacheKey, $sha256, $storeLastModifiedTime];
-
-            return [];
-        }
-
-        return parent::fetchFile($filename, $cacheKey, $sha256, $storeLastModifiedTime);
-    }
-}
diff --git a/src/CurlDownloader.php b/src/CurlDownloader.php
deleted file mode 100644
index 9da133311..000000000
--- a/src/CurlDownloader.php
+++ /dev/null
@@ -1,216 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex;
-
-use Composer\Downloader\TransportException;
-
-/**
- * @author Nicolas Grekas <p@tchwork.com>
- */
-class CurlDownloader
-{
-    private $multiHandle;
-    private $shareHandle;
-    private $jobs = [];
-    private $exceptions = [];
-
-    private static $options = [
-        'http' => [
-            'method' => \CURLOPT_CUSTOMREQUEST,
-            'content' => \CURLOPT_POSTFIELDS,
-        ],
-        'ssl' => [
-            'cafile' => \CURLOPT_CAINFO,
-            'capath' => \CURLOPT_CAPATH,
-        ],
-    ];
-
-    private static $timeInfo = [
-        'total_time' => true,
-        'namelookup_time' => true,
-        'connect_time' => true,
-        'pretransfer_time' => true,
-        'starttransfer_time' => true,
-        'redirect_time' => true,
-    ];
-
-    public function __construct()
-    {
-        $this->multiHandle = $mh = curl_multi_init();
-        curl_multi_setopt($mh, \CURLMOPT_PIPELINING, /*CURLPIPE_MULTIPLEX*/ 2);
-        if (\defined('CURLMOPT_MAX_HOST_CONNECTIONS')) {
-            curl_multi_setopt($mh, \CURLMOPT_MAX_HOST_CONNECTIONS, 8);
-        }
-
-        $this->shareHandle = $sh = curl_share_init();
-        curl_share_setopt($sh, \CURLSHOPT_SHARE, \CURL_LOCK_DATA_COOKIE);
-        curl_share_setopt($sh, \CURLSHOPT_SHARE, \CURL_LOCK_DATA_DNS);
-        curl_share_setopt($sh, \CURLSHOPT_SHARE, \CURL_LOCK_DATA_SSL_SESSION);
-    }
-
-    public function get($origin, $url, $context, $file)
-    {
-        $params = stream_context_get_params($context);
-
-        $ch = curl_init();
-        $hd = fopen('php://temp/maxmemory:32768', 'w+b');
-        if ($file && !$fd = @fopen($file.'~', 'w+b')) {
-            $file = null;
-        }
-        if (!$file) {
-            $fd = @fopen('php://temp/maxmemory:524288', 'w+b');
-        }
-        $headers = array_diff($params['options']['http']['header'], ['Connection: close']);
-
-        if (!isset($params['options']['http']['protocol_version'])) {
-            curl_setopt($ch, \CURLOPT_HTTP_VERSION, \CURL_HTTP_VERSION_1_0);
-        } else {
-            $headers[] = 'Connection: keep-alive';
-            if (0 === strpos($url, 'https://') && \defined('CURL_VERSION_HTTP2') && \defined('CURL_HTTP_VERSION_2_0') && (\CURL_VERSION_HTTP2 & curl_version()['features'])) {
-                curl_setopt($ch, \CURLOPT_HTTP_VERSION, \CURL_HTTP_VERSION_2_0);
-            }
-        }
-
-        curl_setopt($ch, \CURLOPT_URL, $url);
-        curl_setopt($ch, \CURLOPT_HTTPHEADER, $headers);
-        curl_setopt($ch, \CURLOPT_FOLLOWLOCATION, true);
-        curl_setopt($ch, \CURLOPT_DNS_USE_GLOBAL_CACHE, false);
-        curl_setopt($ch, \CURLOPT_WRITEHEADER, $hd);
-        curl_setopt($ch, \CURLOPT_FILE, $fd);
-        curl_setopt($ch, \CURLOPT_SHARE, $this->shareHandle);
-
-        foreach (self::$options as $type => $options) {
-            foreach ($options as $name => $curlopt) {
-                if (isset($params['options'][$type][$name])) {
-                    curl_setopt($ch, $curlopt, $params['options'][$type][$name]);
-                }
-            }
-        }
-
-        $progress = array_diff_key(curl_getinfo($ch), self::$timeInfo);
-        $this->jobs[(int) $ch] = [
-            'progress' => $progress,
-            'ch' => $ch,
-            'callback' => $params['notification'],
-            'file' => $file,
-            'fd' => $fd,
-        ];
-
-        curl_multi_add_handle($this->multiHandle, $ch);
-        $params['notification'](\STREAM_NOTIFY_RESOLVE, \STREAM_NOTIFY_SEVERITY_INFO, '', 0, 0, 0, false);
-        $active = true;
-
-        try {
-            while ($active && isset($this->jobs[(int) $ch])) {
-                curl_multi_exec($this->multiHandle, $active);
-                curl_multi_select($this->multiHandle);
-
-                while ($progress = curl_multi_info_read($this->multiHandle)) {
-                    if (!isset($this->jobs[$i = (int) $h = $progress['handle']])) {
-                        continue;
-                    }
-                    $progress = array_diff_key(curl_getinfo($h), self::$timeInfo);
-                    $job = $this->jobs[$i];
-                    unset($this->jobs[$i]);
-                    curl_multi_remove_handle($this->multiHandle, $h);
-                    try {
-                        $this->onProgress($h, $job['callback'], $progress, $job['progress']);
-
-                        if ('' !== curl_error($h)) {
-                            throw new TransportException(curl_error($h));
-                        }
-                        if ($job['file'] && \CURLE_OK === curl_errno($h) && !isset($this->exceptions[$i])) {
-                            fclose($job['fd']);
-                            rename($job['file'].'~', $job['file']);
-                        }
-                    } catch (TransportException $e) {
-                        $this->exceptions[$i] = $e;
-                    }
-                }
-
-                foreach ($this->jobs as $i => $h) {
-                    if (!isset($this->jobs[$i])) {
-                        continue;
-                    }
-                    $h = $this->jobs[$i]['ch'];
-                    $progress = array_diff_key(curl_getinfo($h), self::$timeInfo);
-
-                    if ($this->jobs[$i]['progress'] !== $progress) {
-                        $previousProgress = $this->jobs[$i]['progress'];
-                        $this->jobs[$i]['progress'] = $progress;
-                        try {
-                            $this->onProgress($h, $this->jobs[$i]['callback'], $progress, $previousProgress);
-                        } catch (TransportException $e) {
-                            unset($this->jobs[$i]);
-                            curl_multi_remove_handle($this->multiHandle, $h);
-                            $this->exceptions[$i] = $e;
-                        }
-                    }
-                }
-            }
-
-            if ('' !== curl_error($ch) || \CURLE_OK !== curl_errno($ch)) {
-                $this->exceptions[(int) $ch] = new TransportException(curl_error($ch), curl_getinfo($ch, \CURLINFO_HTTP_CODE) ?: 0);
-            }
-            if (isset($this->exceptions[(int) $ch])) {
-                throw $this->exceptions[(int) $ch];
-            }
-        } finally {
-            if ($file && !isset($this->exceptions[(int) $ch])) {
-                $fd = fopen($file, 'rb');
-            }
-            $progress = array_diff_key(curl_getinfo($ch), self::$timeInfo);
-            $this->finishProgress($ch, $params['notification'], $progress);
-            unset($this->jobs[(int) $ch], $this->exceptions[(int) $ch]);
-            curl_multi_remove_handle($this->multiHandle, $ch);
-            curl_close($ch);
-
-            rewind($hd);
-            $headers = explode("\r\n", rtrim(stream_get_contents($hd)));
-            fclose($hd);
-
-            rewind($fd);
-            $contents = stream_get_contents($fd);
-            fclose($fd);
-        }
-
-        return [$headers, $contents];
-    }
-
-    private function onProgress($ch, callable $notify, array $progress, array $previousProgress)
-    {
-        if (300 <= $progress['http_code'] && $progress['http_code'] < 400 || 0 > $progress['download_content_length']) {
-            return;
-        }
-
-        if (!$previousProgress['http_code'] && $progress['http_code'] && $progress['http_code'] < 200 || 400 <= $progress['http_code']) {
-            $code = 403 === $progress['http_code'] ? \STREAM_NOTIFY_AUTH_RESULT : \STREAM_NOTIFY_FAILURE;
-            $notify($code, \STREAM_NOTIFY_SEVERITY_ERR, curl_error($ch), $progress['http_code'], 0, 0, false);
-        }
-
-        if ($previousProgress['download_content_length'] < $progress['download_content_length']) {
-            $notify(\STREAM_NOTIFY_FILE_SIZE_IS, \STREAM_NOTIFY_SEVERITY_INFO, '', 0, 0, (int) $progress['download_content_length'], false);
-        }
-
-        if ($previousProgress['size_download'] < $progress['size_download']) {
-            $notify(\STREAM_NOTIFY_PROGRESS, \STREAM_NOTIFY_SEVERITY_INFO, '', 0, (int) $progress['size_download'], (int) $progress['download_content_length'], false);
-        }
-    }
-
-    private function finishProgress($ch, callable $notify, array $progress)
-    {
-        if ($progress['download_content_length'] < 0) {
-            $notify(\STREAM_NOTIFY_FILE_SIZE_IS, \STREAM_NOTIFY_SEVERITY_INFO, '', 0, 0, (int) $progress['size_download'], false);
-            $notify(\STREAM_NOTIFY_PROGRESS, \STREAM_NOTIFY_SEVERITY_INFO, '', 0, (int) $progress['size_download'], (int) $progress['size_download'], false);
-        }
-    }
-}
diff --git a/src/Downloader.php b/src/Downloader.php
index 919d68bb2..a6aeb0167 100644
--- a/src/Downloader.php
+++ b/src/Downloader.php
@@ -11,7 +11,7 @@
 
 namespace Symfony\Flex;
 
-use Composer\Cache as ComposerCache;
+use Composer\Cache;
 use Composer\Composer;
 use Composer\DependencyResolver\Operation\OperationInterface;
 use Composer\DependencyResolver\Operation\UninstallOperation;
@@ -41,8 +41,7 @@ class Downloader
     private $sess;
     private $cache;
 
-    /** @var HttpDownloader|ParallelDownloader */
-    private $rfs;
+    private HttpDownloader $rfs;
     private $degradedMode = false;
     private $endpoints;
     private $index;
@@ -50,7 +49,7 @@ class Downloader
     private $caFile;
     private $enabled = true;
 
-    public function __construct(Composer $composer, IoInterface $io, $rfs)
+    public function __construct(Composer $composer, IoInterface $io, HttpDownloader $rfs)
     {
         if (getenv('SYMFONY_CAFILE')) {
             $this->caFile = getenv('SYMFONY_CAFILE');
@@ -89,7 +88,7 @@ public function __construct(Composer $composer, IoInterface $io, $rfs)
         $this->io = $io;
         $config = $composer->getConfig();
         $this->rfs = $rfs;
-        $this->cache = new ComposerCache($io, $config->get('cache-repo-dir').'/flex');
+        $this->cache = new Cache($io, $config->get('cache-repo-dir').'/flex');
         $this->sess = bin2hex(random_bytes(16));
     }
 
@@ -98,11 +97,6 @@ public function getSessionId(): string
         return $this->sess;
     }
 
-    public function setFlexId(string $id = null)
-    {
-        // No-op to support downgrading to v1.12.x
-    }
-
     public function isEnabled()
     {
         return $this->enabled;
@@ -294,37 +288,19 @@ private function get(array $urls, bool $isRecipe = false, int $try = 3): array
             $options[$url] = $this->getOptions($headers);
         }
 
-        if ($this->rfs instanceof HttpDownloader) {
-            $loop = new Loop($this->rfs);
-            $jobs = [];
-            foreach ($urls as $url) {
-                $jobs[] = $this->rfs->add($url, $options[$url])->then(function (ComposerResponse $response) use ($url, &$responses) {
-                    if (200 === $response->getStatusCode()) {
-                        $cacheKey = self::generateCacheKey($url);
-                        $responses[$url] = $this->parseJson($response->getBody(), $url, $cacheKey, $response->getHeaders())->getBody();
-                    }
-                }, function (\Exception $e) use ($url, &$retries) {
-                    $retries[] = [$url, $e];
-                });
-            }
-            $loop->wait($jobs);
-        } else {
-            foreach ($urls as $i => $url) {
-                $urls[$i] = [$url];
-            }
-            $this->rfs->download($urls, function ($url) use ($options, &$responses, &$retries, &$error) {
-                try {
+        $loop = new Loop($this->rfs);
+        $jobs = [];
+        foreach ($urls as $url) {
+            $jobs[] = $this->rfs->add($url, $options[$url])->then(function (ComposerResponse $response) use ($url, &$responses) {
+                if (200 === $response->getStatusCode()) {
                     $cacheKey = self::generateCacheKey($url);
-                    $origin = method_exists($this->rfs, 'getOrigin') ? $this->rfs::getOrigin($url) : parse_url($url, \PHP_URL_HOST);
-                    $json = $this->rfs->getContents($origin, $url, false, $options[$url]);
-                    if (200 === $this->rfs->findStatusCode($this->rfs->getLastHeaders())) {
-                        $responses[$url] = $this->parseJson($json, $url, $cacheKey, $this->rfs->getLastHeaders())->getBody();
-                    }
-                } catch (\Exception $e) {
-                    $retries[] = [$url, $e];
+                    $responses[$url] = $this->parseJson($response->getBody(), $url, $cacheKey, $response->getHeaders())->getBody();
                 }
+            }, function (\Exception $e) use ($url, &$retries) {
+                $retries[] = [$url, $e];
             });
         }
+        $loop->wait($jobs);
 
         if (!$retries) {
             return $responses;
diff --git a/src/Flex.php b/src/Flex.php
index 0d6913916..7789463c8 100644
--- a/src/Flex.php
+++ b/src/Flex.php
@@ -17,13 +17,9 @@
 use Composer\DependencyResolver\Operation\InstallOperation;
 use Composer\DependencyResolver\Operation\UninstallOperation;
 use Composer\DependencyResolver\Operation\UpdateOperation;
-use Composer\DependencyResolver\Pool;
-use Composer\Downloader\FileDownloader;
 use Composer\EventDispatcher\EventSubscriberInterface;
 use Composer\Factory;
 use Composer\Installer;
-use Composer\Installer\InstallerEvent;
-use Composer\Installer\InstallerEvents;
 use Composer\Installer\PackageEvent;
 use Composer\Installer\PackageEvents;
 use Composer\Installer\SuggestedPackagesReporter;
@@ -32,16 +28,10 @@
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
 use Composer\Package\BasePackage;
-use Composer\Package\Comparer\Comparer;
 use Composer\Package\Locker;
-use Composer\Package\PackageInterface;
 use Composer\Plugin\PluginEvents;
 use Composer\Plugin\PluginInterface;
-use Composer\Plugin\PreFileDownloadEvent;
 use Composer\Plugin\PrePoolCreateEvent;
-use Composer\Repository\ComposerRepository as BaseComposerRepository;
-use Composer\Repository\RepositoryFactory;
-use Composer\Repository\RepositoryManager;
 use Composer\Script\Event;
 use Composer\Script\ScriptEvents;
 use Symfony\Component\Console\Input\ArgvInput;
@@ -78,19 +68,9 @@ class Flex implements PluginInterface, EventSubscriberInterface
     private $postInstallOutput = [''];
     private $operations = [];
     private $lock;
-    private $cacheDirPopulated = false;
     private $displayThanksReminder = 0;
-    private $rfs;
-    private $progress = true;
     private $dryRun = false;
     private static $activated = true;
-    private static $repoReadingCommands = [
-        'create-project' => true,
-        'outdated' => true,
-        'require' => true,
-        'update' => true,
-        'install' => true,
-    ];
     private static $aliasResolveCommands = [
         'require' => true,
         'update' => false,
@@ -123,40 +103,12 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
 
         $symfonyRequire = preg_replace('/\.x$/', '.x-dev', getenv('SYMFONY_REQUIRE') ?: ($composer->getPackage()->getExtra()['symfony']['require'] ?? ''));
 
-        if ($composer2 = version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '<=')) {
-            $rfs = Factory::createHttpDownloader($this->io, $this->config);
+        $rfs = Factory::createHttpDownloader($this->io, $this->config);
 
-            $this->downloader = $downloader = new Downloader($composer, $io, $rfs);
-
-            if ($symfonyRequire) {
-                $this->filter = new PackageFilter($io, $symfonyRequire, $this->downloader);
-            }
+        $this->downloader = $downloader = new Downloader($composer, $io, $rfs);
 
-            $setRepositories = null;
-        } else {
-            $rfs = Factory::createRemoteFilesystem($this->io, $this->config);
-            $this->rfs = $rfs = new ParallelDownloader($this->io, $this->config, $rfs->getOptions(), $rfs->isTlsDisabled());
-
-            $this->downloader = $downloader = new Downloader($composer, $io, $this->rfs);
-
-            $rootPackage = $composer->getPackage();
-            $manager = RepositoryFactory::manager($this->io, $this->config, $composer->getEventDispatcher(), $this->rfs);
-            $setRepositories = \Closure::bind(function (RepositoryManager $manager) use (&$symfonyRequire, $rootPackage, $downloader) {
-                $manager->repositoryClasses = $this->repositoryClasses;
-                $manager->setRepositoryClass('composer', TruncatedComposerRepository::class);
-                $manager->repositories = $this->repositories;
-                $i = 0;
-                foreach (RepositoryFactory::defaultRepos(null, $this->config, $manager) as $repo) {
-                    $manager->repositories[$i++] = $repo;
-                    if ($repo instanceof TruncatedComposerRepository && $symfonyRequire) {
-                        $repo->setSymfonyRequire($symfonyRequire, $rootPackage, $downloader, $this->io);
-                    }
-                }
-                $manager->setLocalRepository($this->getLocalRepository());
-            }, $composer->getRepositoryManager(), RepositoryManager::class);
-
-            $setRepositories($manager);
-            $composer->setRepositoryManager($manager);
+        if ($symfonyRequire) {
+            $this->filter = new PackageFilter($io, $symfonyRequire, $this->downloader);
         }
 
         $this->configurator = new Configurator($composer, $io, $this->options);
@@ -174,21 +126,6 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
             $downloader->disable();
         }
 
-        $populateRepoCacheDir = !$composer2 && __CLASS__ === self::class;
-        if (!$composer2 && $composer->getPluginManager()) {
-            foreach ($composer->getPluginManager()->getPlugins() as $plugin) {
-                if (0 === strpos(\get_class($plugin), 'Hirak\Prestissimo\Plugin')) {
-                    if (method_exists($rfs, 'getRemoteContents')) {
-                        $plugin->disable();
-                    } else {
-                        $this->cacheDirPopulated = true;
-                    }
-                    $populateRepoCacheDir = false;
-                    break;
-                }
-            }
-        }
-
         $backtrace = $this->configureInstaller();
 
         foreach ($backtrace as $trace) {
@@ -207,12 +144,6 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
 
             $resolver = new PackageResolver($this->downloader);
 
-            if (version_compare('1.1.0', PluginInterface::PLUGIN_API_VERSION, '>')) {
-                $note = $app->has('self-update') ? sprintf('`php %s self-update`', $_SERVER['argv'][0]) : 'https://getcomposer.org/';
-                $io->writeError('<warning>Some Symfony Flex features may not work as expected: your version of Composer is too old</>');
-                $io->writeError(sprintf('<warning>Please upgrade using %s</>', $note));
-            }
-
             try {
                 $command = $input->getFirstArgument();
                 $command = $command ? $app->find($command)->getName() : null;
@@ -220,22 +151,13 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
             }
 
             if ('create-project' === $command) {
-                // detect Composer >=1.7 (using the Composer::VERSION constant doesn't work with snapshot builds)
-                if (class_exists(Comparer::class)) {
-                    if ($input->hasOption('remove-vcs')) {
-                        $input->setOption('remove-vcs', true);
-                    }
-                } else {
-                    $input->setInteractive(false);
+                if ($input->hasOption('remove-vcs')) {
+                    $input->setOption('remove-vcs', true);
                 }
-                $populateRepoCacheDir = $populateRepoCacheDir && !$input->hasOption('remove-vcs');
             } elseif ('update' === $command) {
                 $this->displayThanksReminder = 1;
             } elseif ('outdated' === $command) {
                 $symfonyRequire = null;
-                if ($setRepositories) {
-                    $setRepositories($manager);
-                }
             }
 
             if (isset(self::$aliasResolveCommands[$command])) {
@@ -243,20 +165,6 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
                 if ($input->hasArgument('packages')) {
                     $input->setArgument('packages', $resolver->resolve($input->getArgument('packages'), self::$aliasResolveCommands[$command]));
                 }
-
-                if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>') && $input->hasOption('no-suggest')) {
-                    $input->setOption('no-suggest', true);
-                }
-            }
-
-            if (!$composer2) {
-                if ($input->hasParameterOption('--no-progress', true)) {
-                    $this->progress = false;
-                }
-
-                if ($input->hasParameterOption('--dry-run', true)) {
-                    $this->dryRun = true;
-                }
             }
 
             if ($input->hasParameterOption('--prefer-lowest', true)) {
@@ -266,19 +174,11 @@ class_exists(__NAMESPACE__.str_replace('/', '\\', substr($file, \strlen(__DIR__)
                 BasePackage::$stabilities['dev'] = 1 + BasePackage::STABILITY_STABLE;
             }
 
-            if ($populateRepoCacheDir && isset(self::$repoReadingCommands[$command]) && ('install' !== $command || (file_exists($composerFile = Factory::getComposerFile()) && !file_exists(substr($composerFile, 0, -4).'lock')))) {
-                $this->populateRepoCacheDir();
-            }
-
             $app->add(new Command\RequireCommand($resolver, \Closure::fromCallable([$this, 'updateComposerLock'])));
             $app->add(new Command\UpdateCommand($resolver));
             $app->add(new Command\RemoveCommand($resolver));
-            $app->add(new Command\UnpackCommand($resolver));
             $app->add(new Command\RecipesCommand($this, $this->lock, $rfs));
             $app->add(new Command\InstallRecipesCommand($this, $this->options->get('root-dir')));
-            if (class_exists(Command\GenerateIdCommand::class)) {
-                $app->add(new Command\GenerateIdCommand(null));
-            }
             $app->add(new Command\DumpEnvCommand($this->config, $this->options));
 
             break;
@@ -549,7 +449,7 @@ public function uninstall(Composer $composer, IOInterface $io)
     public function enableThanksReminder()
     {
         if (1 === $this->displayThanksReminder) {
-            $this->displayThanksReminder = !class_exists(Thanks::class, false) && version_compare('1.1.0', PluginInterface::PLUGIN_API_VERSION, '<=') ? 2 : 0;
+            $this->displayThanksReminder = !class_exists(Thanks::class, false) ? 2 : 0;
         }
     }
 
@@ -570,124 +470,6 @@ public function executeAutoScripts(Event $event)
         $this->postInstallOutput = [];
     }
 
-    public function populateProvidersCacheDir(InstallerEvent $event)
-    {
-        $listed = [];
-        $packages = [];
-        $pool = $event->getPool();
-        $pool = \Closure::bind(function () {
-            foreach ($this->providerRepos as $k => $repo) {
-                $this->providerRepos[$k] = new class($repo) extends BaseComposerRepository {
-                    private $repo;
-
-                    public function __construct($repo)
-                    {
-                        $this->repo = $repo;
-                    }
-
-                    public function whatProvides(Pool $pool, $name, $bypassFilters = false)
-                    {
-                        $packages = [];
-                        foreach ($this->repo->whatProvides($pool, $name, $bypassFilters) as $k => $p) {
-                            $packages[$k] = clone $p;
-                        }
-
-                        return $packages;
-                    }
-                };
-            }
-
-            return $this;
-        }, clone $pool, $pool)();
-
-        foreach ($event->getRequest()->getJobs() as $job) {
-            if ('install' !== $job['cmd'] || false === strpos($job['packageName'], '/')) {
-                continue;
-            }
-
-            $listed[$job['packageName']] = true;
-            $packages[] = [$job['packageName'], $job['constraint']];
-        }
-
-        $loadExtraRepos = !(new \ReflectionMethod(Pool::class, 'match'))->isPublic(); // Detect Composer < 1.7.3
-        $this->rfs->download($packages, function ($packageName, $constraint) use (&$listed, &$packages, $pool, $loadExtraRepos) {
-            foreach ($pool->whatProvides($packageName, $constraint, true) as $package) {
-                $links = $loadExtraRepos ? array_merge($package->getRequires(), $package->getConflicts(), $package->getReplaces()) : $package->getRequires();
-                foreach ($links as $link) {
-                    if (isset($listed[$link->getTarget()]) || false === strpos($link->getTarget(), '/')) {
-                        continue;
-                    }
-                    $listed[$link->getTarget()] = true;
-                    $packages[] = [$link->getTarget(), $link->getConstraint()];
-                }
-            }
-        });
-    }
-
-    public function populateFilesCacheDir(InstallerEvent $event)
-    {
-        if ($this->cacheDirPopulated || $this->dryRun) {
-            return;
-        }
-        $this->cacheDirPopulated = true;
-
-        $downloads = [];
-        $cacheDir = rtrim($this->config->get('cache-files-dir'), '\/').\DIRECTORY_SEPARATOR;
-        $getCacheKey = function (PackageInterface $package, $processedUrl) {
-            return $this->getCacheKey($package, $processedUrl);
-        };
-        $getCacheKey = \Closure::bind($getCacheKey, new FileDownloader($this->io, $this->config), FileDownloader::class);
-
-        foreach ($event->getOperations() as $op) {
-            if ('install' === $op->getJobType()) {
-                $package = $op->getPackage();
-            } elseif ('update' === $op->getJobType()) {
-                $package = $op->getTargetPackage();
-            } else {
-                continue;
-            }
-
-            if (!$fileUrl = $package->getDistUrl()) {
-                continue;
-            }
-
-            if ($package->getDistMirrors()) {
-                $fileUrl = current($package->getDistUrls());
-            }
-
-            if (!preg_match('/^https?:/', $fileUrl) || !$originUrl = parse_url($fileUrl, \PHP_URL_HOST)) {
-                continue;
-            }
-
-            if (file_exists($file = $cacheDir.$getCacheKey($package, $fileUrl))) {
-                continue;
-            }
-
-            @mkdir(\dirname($file), 0775, true);
-
-            if (!is_dir(\dirname($file))) {
-                continue;
-            }
-
-            if (preg_match('#^https://github\.com/#', $package->getSourceUrl()) && preg_match('#^https://api\.github\.com/repos(/[^/]++/[^/]++/)zipball(.++)$#', $fileUrl, $m)) {
-                $fileUrl = sprintf('https://codeload.github.com%slegacy.zip%s', $m[1], $m[2]);
-            }
-
-            $downloads[] = [$originUrl, $fileUrl, [], $file, false];
-        }
-
-        if (1 < \count($downloads)) {
-            $this->rfs->download($downloads, [$this->rfs, 'get'], false, $this->progress);
-        }
-    }
-
-    public function onFileDownload(PreFileDownloadEvent $event)
-    {
-        if ($event->getRemoteFilesystem() !== $this->rfs) {
-            $event->setRemoteFilesystem($this->rfs->setNextOptions($event->getRemoteFilesystem()->getOptions()));
-        }
-    }
-
     /**
      * @return Recipe[]
      */
@@ -838,40 +620,12 @@ private function shouldRecordOperation(PackageEvent $event): bool
         return false;
     }
 
-    private function populateRepoCacheDir()
-    {
-        $repos = [];
-
-        foreach ($this->composer->getPackage()->getRepositories() as $name => $repo) {
-            if (!isset($repo['type']) || 'composer' !== $repo['type'] || !empty($repo['force-lazy-providers'])) {
-                continue;
-            }
-
-            if (!preg_match('#^http(s\??)?://#', $repo['url'])) {
-                continue;
-            }
-
-            $repo = new ComposerRepository($repo, $this->io, $this->config, null, $this->rfs);
-
-            $repos[] = [$repo];
-        }
-
-        $this->rfs->download($repos, function ($repo) {
-            ParallelDownloader::$cacheNext = true;
-            $repo->getProviderNames();
-        });
-    }
-
     private function updateComposerLock()
     {
         $lock = substr(Factory::getComposerFile(), 0, -4).'lock';
         $composerJson = file_get_contents(Factory::getComposerFile());
         $lockFile = new JsonFile($lock, null, $this->io);
-        if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>')) {
-            $locker = new Locker($this->io, $lockFile, $this->composer->getRepositoryManager(), $this->composer->getInstallationManager(), $composerJson);
-        } else {
-            $locker = new Locker($this->io, $lockFile, $this->composer->getInstallationManager(), $composerJson);
-        }
+        $locker = new Locker($this->io, $lockFile, $this->composer->getInstallationManager(), $composerJson);
         $lockData = $locker->getLockData();
         $lockData['content-hash'] = Locker::getContentHash($composerJson);
         $lockFile->write($lockData);
@@ -929,10 +683,6 @@ private function reinstall(Event $event, bool $update)
             $installer->setUpdateAllowList(['php']);
         }
 
-        if (method_exists($installer, 'setSkipSuggest')) {
-            $installer->setSkipSuggest(true);
-        }
-
         $installer->run();
 
         $this->io->write($this->postInstallOutput);
@@ -949,6 +699,7 @@ public static function getSubscribedEvents(): array
             PackageEvents::POST_PACKAGE_INSTALL => 'record',
             PackageEvents::POST_PACKAGE_UPDATE => [['record'], ['enableThanksReminder']],
             PackageEvents::POST_PACKAGE_UNINSTALL => 'record',
+            PluginEvents::PRE_POOL_CREATE => 'truncatePackages',
             ScriptEvents::POST_CREATE_PROJECT_CMD => 'configureProject',
             ScriptEvents::POST_INSTALL_CMD => 'install',
             ScriptEvents::PRE_UPDATE_CMD => 'configureInstaller',
@@ -956,18 +707,6 @@ public static function getSubscribedEvents(): array
             'auto-scripts' => 'executeAutoScripts',
         ];
 
-        if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>')) {
-            $events += [
-                InstallerEvents::PRE_DEPENDENCIES_SOLVING => [['populateProvidersCacheDir', \PHP_INT_MAX]],
-                InstallerEvents::POST_DEPENDENCIES_SOLVING => [['populateFilesCacheDir', \PHP_INT_MAX]],
-                PackageEvents::PRE_PACKAGE_INSTALL => [['populateFilesCacheDir', ~\PHP_INT_MAX]],
-                PackageEvents::PRE_PACKAGE_UPDATE => [['populateFilesCacheDir', ~\PHP_INT_MAX]],
-                PluginEvents::PRE_FILE_DOWNLOAD => 'onFileDownload',
-            ];
-        } else {
-            $events += [PluginEvents::PRE_POOL_CREATE => 'truncatePackages'];
-        }
-
         return $events;
     }
 
diff --git a/src/PackageJsonSynchronizer.php b/src/PackageJsonSynchronizer.php
index 8d1b2c0ee..282aa8fec 100644
--- a/src/PackageJsonSynchronizer.php
+++ b/src/PackageJsonSynchronizer.php
@@ -228,12 +228,10 @@ private function resolvePackageJson(array $phpPackage): ?JsonFile
      */
     private function compactConstraints(array $constraints): string
     {
-        if (method_exists(Intervals::class, 'isSubsetOf')) {
-            foreach ($constraints as $k1 => $constraint1) {
-                foreach ($constraints as $k2 => $constraint2) {
-                    if ($k1 !== $k2 && Intervals::isSubsetOf($constraint1, $constraint2)) {
-                        unset($constraints[$k2]);
-                    }
+        foreach ($constraints as $k1 => $constraint1) {
+            foreach ($constraints as $k2 => $constraint2) {
+                if ($k1 !== $k2 && Intervals::isSubsetOf($constraint1, $constraint2)) {
+                    unset($constraints[$k2]);
                 }
             }
         }
diff --git a/src/ParallelDownloader.php b/src/ParallelDownloader.php
deleted file mode 100644
index 3acbc3b9b..000000000
--- a/src/ParallelDownloader.php
+++ /dev/null
@@ -1,287 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex;
-
-use Composer\Config;
-use Composer\Downloader\TransportException;
-use Composer\IO\IOInterface;
-use Composer\Util\RemoteFilesystem;
-
-/**
- * Speedup Composer by downloading packages in parallel.
- *
- * @author Nicolas Grekas <p@tchwork.com>
- */
-class ParallelDownloader extends RemoteFilesystem
-{
-    private $io;
-    private $downloader;
-    private $quiet = true;
-    private $progress = true;
-    private $nextCallback;
-    private $downloadCount;
-    private $nextOptions = [];
-    private $sharedState;
-    private $fileName;
-    private $lastHeaders;
-
-    public static $cacheNext = false;
-    protected static $cache = [];
-
-    public function __construct(IOInterface $io, Config $config, array $options = [], $disableTls = false)
-    {
-        $this->io = $io;
-        if (!method_exists(parent::class, 'getRemoteContents')) {
-            $this->io->writeError('Composer >=1.7 not found, downloads will happen in sequence', true, IOInterface::DEBUG);
-        } elseif (!\extension_loaded('curl')) {
-            $this->io->writeError('ext-curl not found, downloads will happen in sequence', true, IOInterface::DEBUG);
-        } else {
-            $this->downloader = new CurlDownloader();
-        }
-        parent::__construct($io, $config, $options, $disableTls);
-    }
-
-    public function download(array &$nextArgs, callable $nextCallback, bool $quiet = true, bool $progress = true)
-    {
-        $previousState = [$this->quiet, $this->progress, $this->downloadCount, $this->nextCallback, $this->sharedState];
-        $this->quiet = $quiet;
-        $this->progress = $progress;
-        $this->downloadCount = \count($nextArgs);
-        $this->nextCallback = $nextCallback;
-        $this->sharedState = (object) [
-            'bytesMaxCount' => 0,
-            'bytesMax' => 0,
-            'bytesTransferred' => 0,
-            'nextArgs' => &$nextArgs,
-            'nestingLevel' => 0,
-            'maxNestingReached' => false,
-            'lastProgress' => 0,
-            'lastUpdate' => microtime(true),
-        ];
-
-        if (!$this->quiet) {
-            if (!$this->downloader && method_exists(parent::class, 'getRemoteContents')) {
-                $this->io->writeError('<warning>Enable the "cURL" PHP extension for faster downloads</>');
-            }
-
-            $note = '';
-            if ($this->io->isDecorated()) {
-                $note = '\\' === \DIRECTORY_SEPARATOR ? '' : (false !== stripos(\PHP_OS, 'darwin') ? '🎵' : '🎶');
-                $note .= $this->downloader ? ('\\' !== \DIRECTORY_SEPARATOR ? ' 💨' : '') : '';
-            }
-
-            $this->io->writeError('');
-            $this->io->writeError(sprintf('<info>Prefetching %d packages</> %s', $this->downloadCount, $note));
-            $this->io->writeError('  - Downloading', false);
-            if ($this->progress) {
-                $this->io->writeError(' (<comment>0%</>)', false);
-            }
-        }
-        try {
-            $this->getNext();
-            if ($this->quiet) {
-                // no-op
-            } elseif ($this->progress) {
-                $this->io->overwriteError(' (<comment>100%</>)');
-            } else {
-                $this->io->writeError(' (<comment>100%</>)');
-            }
-        } finally {
-            if (!$this->quiet) {
-                $this->io->writeError('');
-            }
-            list($this->quiet, $this->progress, $this->downloadCount, $this->nextCallback, $this->sharedState) = $previousState;
-        }
-    }
-
-    public function getOptions()
-    {
-        $options = array_replace_recursive(parent::getOptions(), $this->nextOptions);
-        $this->nextOptions = [];
-
-        return $options;
-    }
-
-    public function setNextOptions(array $options)
-    {
-        $this->nextOptions = parent::getOptions() !== $options ? $options : [];
-
-        return $this;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function getLastHeaders()
-    {
-        return $this->lastHeaders ?? parent::getLastHeaders();
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function copy($originUrl, $fileUrl, $fileName, $progress = true, $options = [])
-    {
-        $options = array_replace_recursive($this->nextOptions, $options);
-        $this->nextOptions = [];
-        $rfs = clone $this;
-        $rfs->fileName = $fileName;
-        $rfs->progress = $this->progress && $progress;
-
-        try {
-            return $rfs->get($originUrl, $fileUrl, $options, $fileName, $rfs->progress);
-        } finally {
-            $rfs->lastHeaders = null;
-            $this->lastHeaders = $rfs->getLastHeaders();
-        }
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function getContents($originUrl, $fileUrl, $progress = true, $options = [])
-    {
-        return $this->copy($originUrl, $fileUrl, null, $progress, $options);
-    }
-
-    /**
-     * @internal
-     */
-    public function callbackGet($notificationCode, $severity, $message, $messageCode, $bytesTransferred, $bytesMax, $nativeDownload = true)
-    {
-        if (!$nativeDownload && \STREAM_NOTIFY_SEVERITY_ERR === $severity) {
-            throw new TransportException($message, $messageCode);
-        }
-
-        parent::callbackGet($notificationCode, $severity, $message, $messageCode, $bytesTransferred, $bytesMax);
-
-        if (!$state = $this->sharedState) {
-            return;
-        }
-
-        if (\STREAM_NOTIFY_FILE_SIZE_IS === $notificationCode) {
-            ++$state->bytesMaxCount;
-            $state->bytesMax += $bytesMax;
-        }
-
-        if (!$bytesMax || \STREAM_NOTIFY_PROGRESS !== $notificationCode) {
-            if ($state->nextArgs && !$nativeDownload) {
-                $this->getNext();
-            }
-
-            return;
-        }
-
-        if (0 < $state->bytesMax) {
-            $progress = $state->bytesMaxCount / $this->downloadCount;
-            $progress *= 100 * ($state->bytesTransferred + $bytesTransferred) / $state->bytesMax;
-        } else {
-            $progress = 0;
-        }
-
-        if ($bytesTransferred === $bytesMax) {
-            $state->bytesTransferred += $bytesMax;
-        }
-
-        if (null !== $state->nextArgs && !$this->quiet && $this->progress && 1 <= $progress - $state->lastProgress) {
-            $progressTime = microtime(true);
-
-            if (5 <= $progress - $state->lastProgress || 1 <= $progressTime - $state->lastUpdate) {
-                $state->lastProgress = $progress;
-                $this->io->overwriteError(sprintf(' (<comment>%d%%</>)', $progress), false);
-                $state->lastUpdate = microtime(true);
-            }
-        }
-
-        if (!$nativeDownload || !$state->nextArgs || $bytesTransferred === $bytesMax || $state->maxNestingReached) {
-            return;
-        }
-
-        if (5 < $state->nestingLevel) {
-            $state->maxNestingReached = true;
-        } else {
-            $this->getNext();
-        }
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function getRemoteContents($originUrl, $fileUrl, $context, array &$responseHeaders = null, $maxFileSize = null)
-    {
-        if (isset(self::$cache[$fileUrl])) {
-            self::$cacheNext = false;
-
-            $result = self::$cache[$fileUrl];
-
-            if (3 < \func_num_args()) {
-                list($responseHeaders, $result) = $result;
-            }
-
-            return $result;
-        }
-
-        if (self::$cacheNext) {
-            self::$cacheNext = false;
-
-            if (3 < \func_num_args()) {
-                $result = $this->getRemoteContents($originUrl, $fileUrl, $context, $responseHeaders, $maxFileSize);
-                self::$cache[$fileUrl] = [$responseHeaders, $result];
-            } else {
-                $result = $this->getRemoteContents($originUrl, $fileUrl, $context);
-                self::$cache[$fileUrl] = $result;
-            }
-
-            return $result;
-        }
-
-        if (!$this->downloader || !preg_match('/^https?:/', $fileUrl)) {
-            return parent::getRemoteContents($originUrl, $fileUrl, $context, $responseHeaders, $maxFileSize);
-        }
-
-        try {
-            $result = $this->downloader->get($originUrl, $fileUrl, $context, $this->fileName);
-
-            if (3 < \func_num_args()) {
-                list($responseHeaders, $result) = $result;
-            }
-
-            return $result;
-        } catch (TransportException $e) {
-            $this->io->writeError('Retrying download: '.$e->getMessage(), true, IOInterface::DEBUG);
-
-            return parent::getRemoteContents($originUrl, $fileUrl, $context, $responseHeaders, $maxFileSize);
-        } catch (\Throwable $e) {
-            $responseHeaders = [];
-            throw $e;
-        }
-    }
-
-    private function getNext()
-    {
-        $state = $this->sharedState;
-        ++$state->nestingLevel;
-
-        try {
-            while ($state->nextArgs && (!$state->maxNestingReached || 1 === $state->nestingLevel)) {
-                try {
-                    $state->maxNestingReached = false;
-                    ($this->nextCallback)(...array_shift($state->nextArgs));
-                } catch (TransportException $e) {
-                    $this->io->writeError('Skipping download: '.$e->getMessage(), true, IOInterface::DEBUG);
-                }
-            }
-        } finally {
-            --$state->nestingLevel;
-        }
-    }
-}
diff --git a/src/ScriptExecutor.php b/src/ScriptExecutor.php
index 967aba97c..69842b3f0 100644
--- a/src/ScriptExecutor.php
+++ b/src/ScriptExecutor.php
@@ -14,7 +14,6 @@
 use Composer\Composer;
 use Composer\EventDispatcher\ScriptExecutionException;
 use Composer\IO\IOInterface;
-use Composer\Semver\Constraint\EmptyConstraint;
 use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Util\ProcessExecutor;
 use Symfony\Component\Console\Output\OutputInterface;
@@ -94,7 +93,7 @@ private function expandCmd(string $type, string $cmd)
     private function expandSymfonyCmd(string $cmd)
     {
         $repo = $this->composer->getRepositoryManager()->getLocalRepository();
-        if (!$repo->findPackage('symfony/console', class_exists(MatchAllConstraint::class) ? new MatchAllConstraint() : new EmptyConstraint())) {
+        if (!$repo->findPackage('symfony/console', new MatchAllConstraint())) {
             $this->io->writeError(sprintf('<warning>Skipping "%s" (needs symfony/console to run).</>', $cmd));
 
             return null;
diff --git a/src/TruncatedComposerRepository.php b/src/TruncatedComposerRepository.php
deleted file mode 100644
index 82485aeaf..000000000
--- a/src/TruncatedComposerRepository.php
+++ /dev/null
@@ -1,44 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex;
-
-use Composer\Config;
-use Composer\EventDispatcher\EventDispatcher;
-use Composer\IO\IOInterface;
-use Composer\Package\RootPackageInterface;
-use Composer\Repository\ComposerRepository as BaseComposerRepository;
-use Composer\Util\RemoteFilesystem;
-
-/**
- * @author Nicolas Grekas <p@tchwork.com>
- */
-class TruncatedComposerRepository extends BaseComposerRepository
-{
-    public function __construct(array $repoConfig, IOInterface $io, Config $config, EventDispatcher $eventDispatcher = null, RemoteFilesystem $rfs = null)
-    {
-        parent::__construct($repoConfig, $io, $config, $eventDispatcher, $rfs);
-
-        $this->cache = new Cache($io, $config->get('cache-repo-dir').'/'.preg_replace('{[^a-z0-9.]}i', '-', $this->url), 'a-z0-9.$');
-    }
-
-    public function setSymfonyRequire(string $symfonyRequire, RootPackageInterface $rootPackage, Downloader $downloader, IOInterface $io)
-    {
-        $this->cache->setSymfonyRequire($symfonyRequire, $rootPackage, $downloader, $io);
-    }
-
-    protected function fetchFile($filename, $cacheKey = null, $sha256 = null, $storeLastModifiedTime = false)
-    {
-        $data = parent::fetchFile($filename, $cacheKey, $sha256, $storeLastModifiedTime);
-
-        return \is_array($data) ? $this->cache->removeLegacyTags($data) : $data;
-    }
-}
diff --git a/src/Unpacker.php b/src/Unpacker.php
index 97482929a..e186e0323 100644
--- a/src/Unpacker.php
+++ b/src/Unpacker.php
@@ -13,14 +13,12 @@
 
 use Composer\Composer;
 use Composer\Config\JsonConfigSource;
-use Composer\DependencyResolver\Pool;
 use Composer\Factory;
 use Composer\IO\IOInterface;
 use Composer\Json\JsonFile;
 use Composer\Json\JsonManipulator;
 use Composer\Package\Locker;
 use Composer\Package\Version\VersionSelector;
-use Composer\Plugin\PluginInterface;
 use Composer\Repository\CompositeRepository;
 use Composer\Repository\RepositorySet;
 use Composer\Semver\VersionParser;
@@ -105,8 +103,7 @@ public function unpack(Operation $op, Result $result = null, &$links = [], bool
 
                         if ('*' === $constraint) {
                             if (null === $versionSelector) {
-                                $pool = class_exists(RepositorySet::class) ? RepositorySet::class : Pool::class;
-                                $pool = new $pool($this->composer->getPackage()->getMinimumStability(), $this->composer->getPackage()->getStabilityFlags());
+                                $pool = new RepositorySet($this->composer->getPackage()->getMinimumStability(), $this->composer->getPackage()->getStabilityFlags());
                                 $pool->addRepository(new CompositeRepository($this->composer->getRepositoryManager()->getRepositories()));
                                 $versionSelector = new VersionSelector($pool);
                             }
@@ -205,11 +202,7 @@ public function updateLock(Result $result, IOInterface $io): void
         }
 
         // force removal of files under vendor/
-        if (version_compare('2.0.0', PluginInterface::PLUGIN_API_VERSION, '>')) {
-            $locker = new Locker($io, $lockFile, $this->composer->getRepositoryManager(), $this->composer->getInstallationManager(), $jsonContent);
-        } else {
-            $locker = new Locker($io, $lockFile, $this->composer->getInstallationManager(), $jsonContent);
-        }
+        $locker = new Locker($io, $lockFile, $this->composer->getInstallationManager(), $jsonContent);
         $this->composer->setLocker($locker);
     }
 }
diff --git a/tests/CacheTest.php b/tests/CacheTest.php
deleted file mode 100644
index 7c25a9ba8..000000000
--- a/tests/CacheTest.php
+++ /dev/null
@@ -1,146 +0,0 @@
-<?php
-
-/*
- * This file is part of the Symfony package.
- *
- * (c) Fabien Potencier <fabien@symfony.com>
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Symfony\Flex\Tests;
-
-use Composer\Package\Link;
-use Composer\Package\RootPackage;
-use Composer\Semver\Constraint\Constraint;
-use PHPUnit\Framework\TestCase;
-use Symfony\Flex\Cache;
-
-class CacheTest extends TestCase
-{
-    /**
-     * @dataProvider provideRemoveLegacyTags
-     */
-    public function testRemoveLegacyTags(array $expected, array $packages, string $symfonyRequire, array $versions)
-    {
-        $downloader = $this->getMockBuilder('Symfony\Flex\Downloader')->disableOriginalConstructor()->getMock();
-        $downloader->expects($this->once())
-            ->method('getVersions')
-            ->willReturn($versions);
-
-        $rootPackage = new RootPackage('test/test', '1.0.0.0', '1.0');
-        $rootPackage->setRequires([
-            'symfony/bar' => new Link('__root__', 'symfony/bar', new Constraint('>=', '3.0.0.0')),
-        ]);
-
-        $cache = (new \ReflectionClass(Cache::class))->newInstanceWithoutConstructor();
-        $cache->setSymfonyRequire($symfonyRequire, $rootPackage, $downloader);
-
-        $this->assertSame(['packages' => $expected], $cache->removeLegacyTags(['packages' => $packages]));
-    }
-
-    public function provideRemoveLegacyTags()
-    {
-        yield 'no-symfony/symfony' => [[123], [123], '~1', ['splits' => []]];
-
-        $branchAlias = function ($versionAlias) {
-            return [
-                'extra' => [
-                    'branch-alias' => [
-                        'dev-main' => $versionAlias.'-dev',
-                    ],
-                ],
-            ];
-        };
-
-        $packages = [
-            'foo/unrelated' => [
-                '1.0.0' => [],
-            ],
-            'symfony/symfony' => [
-                '3.3.0' => ['version_normalized' => '3.3.0.0'],
-                '3.4.0' => ['version_normalized' => '3.4.0.0'],
-                'dev-main' => $branchAlias('3.5'),
-            ],
-            'symfony/foo' => [
-                '3.3.0' => ['version_normalized' => '3.3.0.0'],
-                '3.4.0' => ['version_normalized' => '3.4.0.0'],
-                'dev-main' => $branchAlias('3.5'),
-            ],
-        ];
-
-        yield 'empty-intersection-ignores-2' => [$packages, $packages, '~2.0', ['splits' => [
-            'symfony/foo' => ['3.3', '3.4', '3.5'],
-        ]]];
-        yield 'empty-intersection-ignores-4' => [$packages, $packages, '~4.0', ['splits' => [
-            'symfony/foo' => ['3.3', '3.4', '3.5'],
-        ]]];
-
-        $expected = $packages;
-        unset($expected['symfony/symfony']['3.3.0']);
-        unset($expected['symfony/foo']['3.3.0']);
-
-        yield 'non-empty-intersection-filters' => [$expected, $packages, '~3.4', ['splits' => [
-            'symfony/foo' => ['3.3', '3.4', '3.5'],
-        ]]];
-
-        unset($expected['symfony/symfony']['3.4.0']);
-        unset($expected['symfony/foo']['3.4.0']);
-
-        yield 'main-only' => [$expected, $packages, '~3.5', ['splits' => [
-            'symfony/foo' => ['3.4', '3.5'],
-        ]]];
-
-        $packages = [
-            'symfony/symfony' => [
-                '2.8.0' => ['version_normalized' => '2.8.0.0'],
-            ],
-            'symfony/legacy' => [
-                '2.8.0' => ['version_normalized' => '2.8.0.0'],
-                'dev-main' => $branchAlias('2.8'),
-            ],
-        ];
-
-        yield 'legacy-are-not-filtered' => [$packages, $packages, '~3.0', ['splits' => [
-            'symfony/legacy' => ['2.8'],
-            'symfony/foo' => ['2.8'],
-        ]]];
-
-        $packages = [
-            'symfony/symfony' => [
-                '2.8.0' => ['version_normalized' => '2.8.0.0'],
-                'dev-main' => $branchAlias('3.0'),
-            ],
-            'symfony/foo' => [
-                '2.8.0' => ['version_normalized' => '2.8.0.0'],
-                'dev-main' => $branchAlias('3.0'),
-            ],
-            'symfony/new' => [
-                'dev-main' => $branchAlias('3.0'),
-            ],
-        ];
-
-        $expected = $packages;
-        unset($expected['symfony/symfony']['dev-main']);
-        unset($expected['symfony/foo']['dev-main']);
-
-        yield 'main-is-filtered-only-when-in-range' => [$expected, $packages, '~2.8', ['splits' => [
-            'symfony/foo' => ['2.8', '3.0'],
-            'symfony/new' => ['3.0'],
-        ]]];
-
-        $packages = [
-            'symfony/symfony' => [
-                '3.0.0' => ['version_normalized' => '3.0.0.0'],
-            ],
-            'symfony/bar' => [
-                '3.0.0' => ['version_normalized' => '3.0.0.0'],
-            ],
-        ];
-
-        yield 'root-constraints-are-preserved' => [$packages, $packages, '~2.8', ['splits' => [
-            'symfony/bar' => ['2.8', '3.0'],
-        ]]];
-    }
-}