KfW153 loan immediate repayment - prepayment penalty?

Perhaps an upgrade to KfW40 with little additional effort might be feasible. The new KfW conditions could probably cover the extra cost. As you already mentioned, the share of the energy consultant can also be subsidized to specifically check this.

Maybe your regular bank, where your standard savings account is held, will cooperate?

In case anyone is still considering it: I have contacted two private banks and two Raiffeisen banks/cooperative banks. The private banks dismiss it uninterestedly, the Raiffeisen banks seem very willing to offer it.

Perhaps an upgrade to KfW40 might be feasible with little extra effort. The new KfW conditions could probably cover the additional cost.

The increased subsidy for KfW40 compared to KfW55 has remained the same and was previously already unprofitable for solid construction with monolithic masonry. I assume that KfW55 is now the new "sweet spot" for solid construction. Previously, it was the Energy Saving Ordinance. We just built slightly better out of nonsense.

So it has already been built? Then the issue should be settled?

New from 24.1 are the increase to 120k euros and an increase in the repayment subsidy. In absolute terms, the difference (almost (1000 euros)) remains the same.
How do you build solidly? I have seen construction projects several times that only achieved the jump to KfW40 through more precise recalculations (e.g. of the thermal bridges). The increase in the repayment subsidy easily covered that.

So construction has already started? Then the issue should be settled, right?

It was very inappropriately phrased, construction is yet to begin.

I see no cost advantage in the early repayment of the loan. Why don't you just let it run? If you really don't need the money, you can invest it accordingly and exit even better that way.