6 classes are annotated with CommercePaymentGateway in Commerce Core 8.2

Manual in modules/payment/src/Plugin/Commerce/PaymentGateway/Manual.php

Provides the Manual payment gateway.

OffsiteRedirect in modules/payment_example/src/Plugin/Commerce/PaymentGateway/OffsiteRedirect.php

Provides the Off-site Redirect payment gateway.

Onsite in modules/payment_example/src/Plugin/Commerce/PaymentGateway/Onsite.php

Provides the On-site payment gateway.

StoredOffsiteRedirect in modules/payment_example/src/Plugin/Commerce/PaymentGateway/StoredOffsiteRedirect.php

Provides an example offsite payment gateway with stored payment methods.

TestOffsite in modules/payment/tests/modules/commerce_payment_test/src/Plugin/Commerce/PaymentGateway/TestOffsite.php

Provides the Test off-site payment gateway.

TestOnsite in modules/payment/tests/modules/commerce_payment_test/src/Plugin/Commerce/PaymentGateway/TestOnsite.php

Provides the Test on-site payment gateway.