  We present an ACA search for [CI] emission at 492GHz toward large T Tauri
disks (gas radii $\gtrsim 200$au) in the $\sim 1-3$Myr-old Lupus star-forming
region. Combined with ALMA 12-m archival data for IM Lup, we report [CI]
detections in 6 out of 10 sources, thus doubling the known detections toward T
Tauri disks. We also identify four Keplerian double-peaked profiles and
demonstrate that [CI] fluxes correlate with $^{13}$CO, C$^{18}$O, and
$^{12}$CO(2-1) fluxes, as well as with the gas disk outer radius measured from
the latter transition. These findings are in line with the expectation that
atomic carbon traces the disk surface. In addition, we compare the carbon and
CO line luminosities of the Lupus and literature sample with [CI] detections
with predictions from the self-consistent disk thermo-chemical models of Ruaud
et al. (2022). These models adopt ISM carbon and oxygen elemental abundances as
input parameters. With the exception of the disk around Sz 98, we find that
these models reproduce all available line luminosities and upper limits with
gas masses comparable to or higher than the minimum mass solar nebula and
gas-to-dust mass ratios $\geq 10$. Thus, we conclude that the majority of large
Myr-old disks conform to the simple expectation that they are not significantly
depleted in gas, CO, or carbon.
