X-OCN stands for "eXtended tonal range Original Camera Negative".

The enormous advantages of RAW recordings such as full flexibility in the post and excellent image quality are countered by unwieldy large amounts of data with large storage requirements and long copying times. The X-OCN format introduced by Sony meets these challenges without compromising the benefits of RAW recording.
X-OCN stands for "eXtended tonal range Original Camera Negative". Data available in two compression rates and packed in MXF containers represent the entire sensor output with its dynamic range on the one hand, and on the other hand the data are economically compressed with an algorithm that, according to Sony, has been tuned to the F5/55 . Settings for sensitivity (ISO ) and color temperature are stored in the metadata and remain available for subsequent processing.
According to Sony, there is no visual difference between standard compression (ST) and F-55 RAW - considering a reduction in data volume of up to 60%. The second available compression format is X-OCN Light (LT) and compresses more than the standard format. Compared to the standard Sony RAW of the F-55, the storage volumes are remarkably reduced. Using a 1TB memory card to record 4K at 24fps is enough for 120 minutes with RAW recording, but 168 minutes with X-OCN ST compression. And if you choose X-OCN LT, then it is 284 minutes for 1TB memory requirement.

[center]X-OCN Bit Rate Comparison - Credit: Sony

The internal storage of X-OCN in the F-5/55 is not possible. This compression format requires the AXS-R7 docking recorder. For this purpose the memory cards of the AXS A series can be used. For a 120fps fast recording in 4K, both RAW and X-OCN require the faster type S48. 
X-OCN Summary

- Quantization: 16 Bit
- File format: MXF
- Versions: Standard (ST), Light (LT)
- Storage: only with AXS-R7 docking recorder on AXS-A cards
- Reduction of transfer times to approx. 60%.