Yes, the Lexar Professional CFexpress Type A Gold 256GB is compatible with the Sony FX3.
Sony FX3's highest-bitrate movie mode, XAVC S-I 4K (600Mbps), requires a CFexpress Type A memory card rated VPG200 or higher per Sony's own Help Guide. Lexar Professional CFexpress Type A Gold 256GB is VPG400-certified per Lexar's own product page -- exceeds the VPG200 floor by a full class. Type A slot confirmed on FX3.
“Capacity 256GB. Key Features: Up to 1800MB/s read, 1650MB/s write speeds. Sustained write speed 1000MB/s. VPG400 Certified.”
“This camera supports CFexpress Type A memory cards and SD memory cards (UHS-I, UHS-II compatible).”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)