Please find my comments in the supplementary PDF file.

The work reviews the hydrogen solubility in SiO2 stishovite and the implication behind it. I like to read it and I think the authors took in consideration all the relevant literature to write down such review. I also liked that they also proposed a new possible equation for calculating the solubility of hydrogen in stishovite. The work is written very well and the science is sound. So I recommend to publish it with only very minor corrections, which are reported here below.

Line 34-36. Well, here I would definitively cite Gu et al. (2022) Nature Geoscience, who showed that coesite (former stishovite) was present within a natural super-deep diamond formed at the boundary between the transition zone and the lower mantle.

Line 51. Please use the accepted nomenclature for space groups (so the Bravais lattice, and the glade and mirror planes must be reported in Italic)

Line 215. “Gavrilenko (2008)” instead of “Gavrilenko, 2008 showed…”

I have doubled checked the references and I only found the following minor issues:

- Bolfan-Casanova et al., 2000 (in Table 1) is mentioned in the text but is missing in the reference list

- Stishov and Popova (1961) is not quoted in the reference list

- Yin and Kang, 2023 check with the journal if this can be reported

This manuscript delivers a comprehensive review of the controlling factors and incorporation mechanism influencing water solubility in stishovite. Furthermore, building on published findings, it introduces a novel equation for estimating water solubility in Al-bearing stishovite. The manuscript is generally well-structured, and the presented results are robust. The discussion regarding the role of water in stishovite contributing to the presence of a water-rich transition zone appears sound. Therefore, I recommend its publication in Solid Earth after some revisions.

I have only the following minor concerns and suggestions on the presentation of results and interpretations.

• Page 2, line 47. “Under average geothermal gradient”. The average geothermal gradient mentioned here is often associated with specific geological settings. I assume the authors are referring to the temperature profile along the surface of oceanic subducting slab. It needs clarification, and the different types of subduction zones (cold subduction, hot subduction) should be labeled on Figure 3. Another simpler approach could be to mark the geotherms of 5 degrees Celsius/km, 10 degrees Celsius/km, and 15 degrees Celsius/km, respectively, on Figure 3.
• Page 3. Figure 2. The data source for the red geotherm curve needs to be indicated.
• Page 3. Line 64. “only found”. It may not be accurate. Yang J.S. et al. (2007, Geology, doi: 10.1130/G23766A.1) identified polycrystalline coesite as a potential pseudomorphic replacement of stishovite in Tibetan chromitites. Therefore, it is preferable to omit the word "only."
• Page 10. Figure 6. Here, the mantle transition zone is only associated with pressure. In reality, the temperature in the mantle transition zone may be around 1400-1600 degrees Celsius (Ito & Katsura, GRL, 1989), exceeding the temperature range calculated in the figure. If you want to correspond to the temperature and pressure of the subducting slabs in the mantle transition zone depths, it would be necessary to separately label the temperature and pressure ranges for different types (cold and hot) of subducting slabs.
• Page 10. Line 224. “along the geotherm”. The term "geotherm" here needs clarification to specify what exactly is meant by "geotherm" (mantle geotherm or subduction zone geotherm).
• Page 11. Figure 7. In Zheng et al. (2016), four distinct geotherms (ultracold subduction, cold subduction, warm subduction, and hot subduction) are identified. It is essential to specify which geotherm was employed and provide a rationale for the choice. Considering the comprehensive coverage, it might be more beneficial to utilize the full range of geotherms to encompass variations.
• The language expression in this paper is overall very good, but there are still some places that may need modification. I have made some annotated suggestions in the attached PDF file for the authors' reference.