fiducial_params = {
    "ombh2": 0.022,
    "omch2": 0.12,
    "H0": 68,
    "tau": 0.07,
    "As": 2.2e-9,
    "ns": 0.96,
    "mnu": 0.06,
    "nnu": 3.046,
}

l_max = 1000

packages_path = "/path/to/your/packages"

info_fiducial = {
    "params": fiducial_params,
    "likelihood": {"one": None},
    "theory": {"camb": {"extra_args": {"num_massive_neutrinos": 1}}},
    "packages_path": packages_path,
}

from cobaya.model import get_model

model_fiducial = get_model(info_fiducial)

# Declare our desired theory product
# (there is no cosmological likelihood doing it for us)
model_fiducial.add_requirements({"Cl": {"tt": l_max}})

# Compute and extract the CMB power spectrum
# (In muK^-2, without l(l+1)/(2pi) factor)
# notice the empty dictionary below: all parameters are fixed
model_fiducial.logposterior({})
Cls = model_fiducial.provider.get_Cl(ell_factor=False, units="muK2")

# Our fiducial power spectrum
Cl_est = Cls["tt"][: l_max + 1]
