The authors present a thorough overview of the changes included in the updated version of the regional climate model RACMO, with many improvements tuned for the polar regions.

Evaluation includes comparison against comprehensive meteorological station datasets, but is otherwise mostly focusing on comparisons with the previous model version. While that indirectly (via articles referred to in the paper of evaluation of the previous version) enables comparison against remote sensing datasets, it would have been nice to see some figures where spatial patterns can be more closely examined for both model versions, for example against the mentioned CALIOP/CALIPSO dataset, or maybe MODIS or CLARA? Noting that the use of satellite data in the polar regions has its own issues (few near-pole overpasses, persistent cloud cover, lack of in-situ data for validation etc.) I think the current approach is fine.

All in all, I find the manuscript well-written with a good structure and sound conclusions.

I have only a few minor comments before I can recommend accepting it:

L67-68: Please explain a little bit more what "flexibility" refers to in the sentence "recoded in order to improve code readability and flexibility". Does it for example include code refactoring, or make it easier to adapt to heterogeneous hardware in the future?

L254-255: If I understood it correctly, you use fractional glacier cover. Does the sentence "Only measurement sites that are also located on a glaciated grid point in RACMO are included in this study" mean you are using cells with 100% glacier cover, or another threshold?

L266: Please motivate why the exclusion threshold is set as low as one missing hour per day. It sounds a bit aggressive to me, but perhaps there are very few days with only a few hours missing.

L342-343: MAR results are not shown for comparison. Consider being more explicit, for example "compare Fig. 3a with Fig. X of Fettweis et al. 2020", or adding "(not shown)", or dropping this sentence entirely.

I would personally prefer to have some of the figures use inverted colour scales, so that blue would indicate more water/snow/ice (in analogy with cooler temperature being illustrated with blue color) and red for less.

This applies to Figures 2, 3b, 8b and 10.

I can see that you may want to use red for positive changes for consistency (e.g. in Fig. 5 where you use the same colourbar for all panels), so I don't insist on you to take this comment into account.

Typos:

L90: M in model should not be capitalised.

L379: "such S6 or S7" -> "such as S6 or S7"

L450: "Between -80 to -40 °C" -> "Between -80 and -40 °C"

In the paper by van Dalum et al., a thorough description is presented of the newest version of the polar regional climate model RACMO, version 2.4. The model is described, and a comparison is presented with the previous version and with observations.

The paper is very well written, the descriptions are thorough though still easily readable, and the results are well presented. It is recommended to be published after a very few adaptations.

Further,  the results look very promising, particularly the effects of snow advection.

In Section 6, there are quantitative estimates of model bias for Arctic snow depth; it would improve the paper if some more qualitative considerations would be added: Is the current model good enough for intended uses related to this field? What are relative errors, etc. You might also consider to move this (Arctic) section before the Antarctic Section 5.

Minor comment: There seems to be no reference to Table 2 in the text even though numbers from the table are discussed.