Increasing Ethereum's block gas limit from 36 million to 60 million units can be implemented without a hard fork, as validators are able to apply the change by modifying their node configurations during block proposal.

Quotes that support claims

Unlike other upgrades, such as Pectra, this change would not require a hard fork. It can be adjusted by Validators through node configuration while proposing blocks.

Unlike major protocol upgrades, this change does not require a hard fork. Validators can adjust their node configurations when proposing blocks.