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##  Appendix A Subtracted Images

Figure 12: As in Figure 3, except for the NIRCam F250M, F300M, F356W, F410M,
and F444W filters. Here we show subtractions using the maximum number of PCA
modes for ADI, RDI, and ADI+RDI, respectively. The F250M subtracted images
have been smoothed as described in Section 2. Figure 13: As in Figure 3,
except for the MIRI F1140C and F1550C filters. Here we show subtractions using
the maximum number of PCA modes for ADI, RDI, and ADI+RDI, respectively. To
aid visual clarity, the subtracted F1550C images are shown with a peak image
intensity five times smaller than the unsubtracted image.

##  Appendix B Contrast Performance

Figure 14: As in Figure 5, but for all used filters. We also plot the
equivalent predicted contrast curves for these observations from PanCAKE (grey
lines) following (Carter et al., 2021b). In every filter JWST is exceeding its
predicted performance.

##  Appendix C PSF Fitting

Figure 15: The data (left column), model PSF (middle column), and residuals
(right column) for the spaceKLIP PSF fitting of the NIRCam observations of HIP
65426 b. Pixel counts are in MJy/sr and are indicated by the colour bar on the
right hand side, images are oriented with North upwards and North through East
counterclockwise, and the image size is 30$\times$30 pixels (1.9$\times$1.9″).
Figure 16: As in Figure 15, but for the MIRI observations. The image size is
30$\times$30 pixels (3.3$\times$3.3″).

##  Appendix D Complementary photometric measurements of HIP 65426 b

Table 4: Additional photometric measurements of HIP 65426 b considered in this
work.

Wavelength ($\mu$m) | Bandwidth ($\mu$m) | Instrument | Band | Flux (W m${}^{-2}\mu$m-1) | Ref.
---|---|---|---|---|---
1.002 | 0.011 | SPHERE/IFS | YJ | $(2.434\pm 0.569)\times 10^{-17}$ | 1
1.011 | 0.011 | SPHERE/IFS | YJ | $(3.155\pm 0.670)\times 10^{-17}$ | 1
1.021 | 0.011 | SPHERE/IFS | YJ | $(3.564\pm 0.575)\times 10^{-17}$ | 1
1.030 | 0.011 | SPHERE/IFS | YJ | $(3.199\pm 0.428)\times 10^{-17}$ | 1
1.040 | 0.011 | SPHERE/IFS | YJ | $(4.095\pm 0.482)\times 10^{-17}$ | 1
1.050 | 0.011 | SPHERE/IFS | YJ | $(3.829\pm 0.435)\times 10^{-17}$ | 1
1.060 | 0.011 | SPHERE/IFS | YJ | $(4.154\pm 0.489)\times 10^{-17}$ | 1
1.070 | 0.011 | SPHERE/IFS | YJ | $(4.456\pm 0.521)\times 10^{-17}$ | 1
1.081 | 0.011 | SPHERE/IFS | YJ | $(4.679\pm 0.432)\times 10^{-17}$ | 1
1.091 | 0.011 | SPHERE/IFS | YJ | $(5.143\pm 0.483)\times 10^{-17}$ | 1
1.102 | 0.011 | SPHERE/IFS | YJ | $(4.746\pm 0.543)\times 10^{-17}$ | 1
1.112 | 0.011 | SPHERE/IFS | YJ | $(5.127\pm 0.576)\times 10^{-17}$ | 1
1.123 | 0.011 | SPHERE/IFS | YJ | $(4.775\pm 0.641)\times 10^{-17}$ | 1
1.133 | 0.011 | SPHERE/IFS | YJ | $(5.228\pm 0.682)\times 10^{-17}$ | 1
1.144 | 0.011 | SPHERE/IFS | YJ | $(4.982\pm 0.609)\times 10^{-17}$ | 1
1.154 | 0.011 | SPHERE/IFS | YJ | $(4.821\pm 0.519)\times 10^{-17}$ | 1
1.165 | 0.011 | SPHERE/IFS | YJ | $(5.324\pm 0.486)\times 10^{-17}$ | 1
1.175 | 0.011 | SPHERE/IFS | YJ | $(4.739\pm 0.453)\times 10^{-17}$ | 1
1.186 | 0.011 | SPHERE/IFS | YJ | $(5.709\pm 0.477)\times 10^{-17}$ | 1
1.196 | 0.011 | SPHERE/IFS | YJ | $(5.291\pm 0.415)\times 10^{-17}$ | 1
1.206 | 0.011 | SPHERE/IFS | YJ | $(6.155\pm 0.471)\times 10^{-17}$ | 1
1.217 | 0.011 | SPHERE/IFS | YJ | $(6.586\pm 0.490)\times 10^{-17}$ | 1
1.227 | 0.011 | SPHERE/IFS | YJ | $(6.431\pm 0.500)\times 10^{-17}$ | 1
1.237 | 0.011 | SPHERE/IFS | YJ | $(6.203\pm 0.483)\times 10^{-17}$ | 1
1.247 | 0.011 | SPHERE/IFS | YJ | $(6.409\pm 0.477)\times 10^{-17}$ | 1
1.257 | 0.011 | SPHERE/IFS | YJ | $(7.100\pm 0.483)\times 10^{-17}$ | 1
1.266 | 0.011 | SPHERE/IFS | YJ | $(7.289\pm 0.502)\times 10^{-17}$ | 1
1.276 | 0.011 | SPHERE/IFS | YJ | $(7.344\pm 0.504)\times 10^{-17}$ | 1
1.285 | 0.011 | SPHERE/IFS | YJ | $(7.315\pm 0.499)\times 10^{-17}$ | 1
1.294 | 0.011 | SPHERE/IFS | YJ | $(8.215\pm 0.543)\times 10^{-17}$ | 1
1.303 | 0.011 | SPHERE/IFS | YJ | $(8.701\pm 0.543)\times 10^{-17}$ | 1
1.312 | 0.011 | SPHERE/IFS | YJ | $(8.731\pm 0.580)\times 10^{-17}$ | 1
1.321 | 0.011 | SPHERE/IFS | YJ | $(7.450\pm 0.594)\times 10^{-17}$ | 1
1.329 | 0.011 | SPHERE/IFS | YJ | $(7.073\pm 0.583)\times 10^{-17}$ | 1
0.987 | 0.019 | SPHERE/IFS | YJH | $(1.556\pm 0.312)\times 10^{-17}$ | 1
1.002 | 0.019 | SPHERE/IFS | YJH | $(1.791\pm 0.355)\times 10^{-17}$ | 1
1.018 | 0.019 | SPHERE/IFS | YJH | $(2.855\pm 0.510)\times 10^{-17}$ | 1
1.034 | 0.019 | SPHERE/IFS | YJH | $(2.615\pm 0.305)\times 10^{-17}$ | 1
1.051 | 0.019 | SPHERE/IFS | YJH | $(3.394\pm 0.442)\times 10^{-17}$ | 1
1.068 | 0.019 | SPHERE/IFS | YJH | $(4.239\pm 0.456)\times 10^{-17}$ | 1
1.086 | 0.019 | SPHERE/IFS | YJH | $(3.472\pm 0.407)\times 10^{-17}$ | 1
1.104 | 0.019 | SPHERE/IFS | YJH | $(3.802\pm 0.415)\times 10^{-17}$ | 1
1.122 | 0.019 | SPHERE/IFS | YJH | $(4.403\pm 0.504)\times 10^{-17}$ | 1
1.140 | 0.019 | SPHERE/IFS | YJH | $(3.906\pm 0.397)\times 10^{-17}$ | 1
1.159 | 0.019 | SPHERE/IFS | YJH | $(4.132\pm 0.422)\times 10^{-17}$ | 1
1.178 | 0.019 | SPHERE/IFS | YJH | $(4.641\pm 0.452)\times 10^{-17}$ | 1
1.197 | 0.019 | SPHERE/IFS | YJH | $(5.368\pm 0.544)\times 10^{-17}$ | 1
1.216 | 0.019 | SPHERE/IFS | YJH | $(6.356\pm 0.573)\times 10^{-17}$ | 1
1.235 | 0.019 | SPHERE/IFS | YJH | $(6.763\pm 0.602)\times 10^{-17}$ | 1
1.255 | 0.019 | SPHERE/IFS | YJH | $(7.107\pm 0.622)\times 10^{-17}$ | 1
1.274 | 0.019 | SPHERE/IFS | YJH | $(7.228\pm 0.630)\times 10^{-17}$ | 1
1.294 | 0.019 | SPHERE/IFS | YJH | $(7.599\pm 0.668)\times 10^{-17}$ | 1
1.314 | 0.019 | SPHERE/IFS | YJH | $(7.296\pm 0.648)\times 10^{-17}$ | 1
1.333 | 0.019 | SPHERE/IFS | YJH | $(6.046\pm 0.577)\times 10^{-17}$ | 1
1.353 | 0.019 | SPHERE/IFS | YJH | $(5.400\pm 0.649)\times 10^{-17}$ | 1
1.372 | 0.019 | SPHERE/IFS | YJH | $(5.523\pm 0.872)\times 10^{-17}$ | 1
1.391 | 0.019 | SPHERE/IFS | YJH | $(5.875\pm 0.729)\times 10^{-17}$ | 1
1.411 | 0.019 | SPHERE/IFS | YJH | $(5.285\pm 0.550)\times 10^{-17}$ | 1
1.430 | 0.019 | SPHERE/IFS | YJH | $(4.516\pm 0.460)\times 10^{-17}$ | 1
1.449 | 0.019 | SPHERE/IFS | YJH | $(4.768\pm 0.439)\times 10^{-17}$ | 1
1.467 | 0.019 | SPHERE/IFS | YJH | $(5.374\pm 0.484)\times 10^{-17}$ | 1
1.486 | 0.019 | SPHERE/IFS | YJH | $(5.888\pm 0.506)\times 10^{-17}$ | 1
1.504 | 0.019 | SPHERE/IFS | YJH | $(5.927\pm 0.498)\times 10^{-17}$ | 1
1.522 | 0.019 | SPHERE/IFS | YJH | $(6.259\pm 0.519)\times 10^{-17}$ | 1
1.539 | 0.019 | SPHERE/IFS | YJH | $(6.778\pm 0.561)\times 10^{-17}$ | 1
1.556 | 0.019 | SPHERE/IFS | YJH | $(7.318\pm 0.605)\times 10^{-17}$ | 1
1.573 | 0.019 | SPHERE/IFS | YJH | $(7.560\pm 0.624)\times 10^{-17}$ | 1
1.589 | 0.019 | SPHERE/IFS | YJH | $(8.037\pm 0.665)\times 10^{-17}$ | 1
1.605 | 0.019 | SPHERE/IFS | YJH | $(8.497\pm 0.706)\times 10^{-17}$ | 1
1.621 | 0.019 | SPHERE/IFS | YJH | $(8.579\pm 0.715)\times 10^{-17}$ | 1
1.636 | 0.019 | SPHERE/IFS | YJH | $(9.011\pm 0.762)\times 10^{-17}$ | 1
1.593 | 0.055 | SPHERE/IRDIS | H2 | $(8.569\pm 0.383)\times 10^{-17}$ | 1
1.667 | 0.056 | SPHERE/IRDIS | H3 | $(10.129\pm 0.564)\times 10^{-17}$ | 1
2.110 | 0.102 | SPHERE/IRDIS | K1 | $(7.500\pm 0.600)\times 10^{-17}$ | 1
2.251 | 0.109 | SPHERE/IRDIS | K2 | $(7.100\pm 0.600)\times 10^{-17}$ | 1
3.800 | 0.620 | NACO | L’ | $(4.010\pm 0.542)\times 10^{-17}$ | 2, 3
4.051 | 0.020 | NACO | NB4.05 | $(3.220\pm 0.780)\times 10^{-17}$ | 3
4.780 | 0.590 | NACO | M’ | $(2.549\pm 0.820)\times 10^{-17}$ | 2, 3

References. — (1) Chauvin et al. (2017); (2) Cheetham et al. (2019); (3)
Stolker et al. (2020b).

Note. — For the $L^{\prime}$ and $M^{\prime}$-band photometry, we considered
the average of the measurements reported in Cheetham et al. (2019) and Stolker
et al. (2020b), but kept the largest error bars.