---
title: One extension for several X4 versions
summary: Exact ext_v900 catalogs versus cumulative ext_01_diff_v900 layers.
section: tools
kind: guide
status: reference
updated: 2026-10-27
tags: ["X4","modding","version","catalogs"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/Multi-version%20extensions/"]
---
## Choose the layer


| CAT/DAT pair | Applied when |
| --- | --- |
| `ext_01` | Shared content |
| `ext_v900` | Exact 9.00 only, above numbered ext catalogs |
| `subst_v900` | Equivalent exact variant for subst |
| `ext_01_diff_v900` | From 9.00 upward, over existing ext_01; introduced in 9.00 |


`ext_v900` does not mean “9.00 or newer”. A diff catalog requires its numbered base. An exact version layer outranks diff layers.



## Plan your package


An independent packaging plan, not a ready archive:



```text
ext_01:              ui/wiki_panel.lua -> common implementation
ext_v800:            ui/wiki_panel.lua -> 8.00 implementation
ext_01_diff_v900:    ui/wiki_panel.lua -> implementation from 9.00
content.xml:        minimum supported game version
```



Register one stable UI path rather than a missing `panel_900.lua`. For this plan, expect the exact variant on 8.00 and the diff variant on 9.00. A later game may still require code changes even when it loads the catalog.



## Verification


Identify the selected file with a distinct diagnostic marker in every supported game. Record its full version and repeat the UI action. An existing archive does not prove compatibility.



Pack with [X Catalog Tool](wiki:tool-catalog), keeping `content.xml` outside. These rules come from the primary author's investigation; this wiki has not repeated that game experiment.