The submitted manuscript is well written and presents a new methodological approach and algorithm for in situ (U–Th–Sm)/He dating of apatite aimed at reconstructing thermal histories of individual grains. Using apatite samples from southern Germany, the authors demonstrate that the proposed methodology enables the derivation of “He diffusion” profiles. It is shown that profiles corrected for parent nuclide distribution are flat in rapidly cooled grain, whereas in samples with heterogeneous parent nuclide distribution and complex thermochronological history, they exhibit non-flat geometries. It is shown how the obtained analytical data can be mathematically processed to derive information on the thermal history of the grains.

Thus, I consider this study to represent a valuable advancement in the development of in situ (U–Th–Sm)/He thermochronology.

My major concern is that the authors did not succeed in deriving a thermochronological path that adequately fits their observations for the BaF apatite. The obtained 4 profiles are reproducible and, as the authors noted, exhibit a counterintuitive geometry: the central part of the grain is significantly younger than the rims.

When the data contradict the model, it typically indicates either low-quality measurements (which I assume is not the case here) or that the model itself may not be correct. Thus, this issue should be discussed in detail. Why did the classical He-loss model fail to reproduce the results? The authors provide only a brief discussion of this matter. Among the factors considered are the presence of inclusions, uranium-enriched zones, and variations in the degree of crystallinity. However, as it was already mentioned, profiles are reproducible, no inclusions are observed in the analyzed half of the grain, and the effect of apatite crystallinity on helium diffusion is limited. The possible influence of implanted helium is not addressed.

This point is of critical importance—if the model does not accurately describe observed in situ (U-Th-Sm)/He profiles, its validity as a basis for thermal history modeling becomes questionable.

General comments

• For a study of this kind, it would have been preferable to use apatite grains from thermochronologically well-characterized localities, where FT and AHe ages are already available, or where even 4He/3He profiles have been obtained. While this may not be essential from a methodological point of view, it would undoubtedly strengthen the testing and validation of the proposed thermochronological modeling approach.
• Sample preparation involved SEM imaging and mounting in Teflon, both of which exposed the samples to elevated temperatures.  The authors likely used low current values for SEM imaging and low temperatures for mounting to limit possible thermal effects; thus, it should not affect the AHe ages. But detailed information regarding this issue should be presented in the methodological section. 
• What are the reasons for the significant variations in He extraction pit depth observed within a single grain (for example, from 6.9 to 9.3 µm; approximately 25%; Table 3)? If the laser energy is dissipated/reflected, could it potentially heat the sample (mobilize He) or heat internal parts of the cell (increase blank level)?

Additional minor comments can be found within the attached file.

Please find my review in the attached file.