Yes, the Lexar Professional 1667x 64GB SD is compatible with the Sony Alpha A9 III.
Lexar Professional 1667x 64GB SD is V60 class. Clears: XAVC S HD (100 Mbps, requires U3); XAVC HS 4K (280 Mbps, requires V60); XAVC S 4K (280 Mbps, requires V60). Does not meet the floor for: XAVC S-I 4K (600 Mbps, requires V90); XAVC S-I HD (222 Mbps, requires V90).
Limitation
Compatible with standard XAVC HS 4K (280Mbps), XAVC S 4K (280Mbps), and XAVC S HD (100Mbps) -- all require V60 or lower. Cannot record XAVC S-I 4K (600Mbps, requires V90) or XAVC S-I HD (222Mbps, requires V90). Upgrade to V90 for intra-frame recording.
“XAVC HS 4K / XAVC S 4K SDXC V60 or higher XAVC S HD SDHC/SDXC card (U3 or higher) XAVC S-I 4K / XAVC S-I HD SDXC V90 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)