  The most salient generic feature of a composite Higgs boson resides in the
nonlinearity of its dynamics, which arises from degenerate vacua associated
with the pseudo-Nambu-Goldstone (PNGB) nature of the Higgs boson. It has been
shown that the nonlinear Higgs dynamics is universal in the IR and controlled
only by a single parameter $f$, the decay constant of the PNGB Higgs. In this
work we perform a fit, for the first time, to Wilson coefficients of ${\cal
O}(p^4)$ operators in the nonlinear Lagrangian using the golden H $\to$ 4L
decay channel. By utilizing both the "rate" information in the signal strength
and the "shape" information in the fully differential spectra, we provide
limits on the Goldstone decay constant $f$, as well as ${\cal O}(p^4)$ Wilson
coefficients, using Run 2 data at the LHC. In rate measurements alone, the
golden channel prefers a negative $\xi =v^2/f^2$ corresponding to a non-compact
coset structure. Including the shape information, we identify regions of
parameter space where current LHC constraint on $f$ is still weak, allowing for
$\xi \lesssim 0.5$ or $\xi \gtrsim -0.5$. We also comment on future sensitivity
at the high-luminosity upgrade of the LHC which could allow for simultaneous
fits to multiple Wilson coefficients.
