Multiclass progression
Multiclass characters gain power levels every three character levels and cannot access ability levels 8 or 9 in either selected class.
How it works
The class passage says multiclass characters gain a power level every three levels, compared with every two for single-class characters. Ability tiers unlock with power levels, so the source says multiclass characters reach higher tiers later. It also states that multiclass characters cannot access ability levels 8 or 9 in either class and gain a power-source point for both classes every three levels. These are the passage’s general rules; edition-specific exceptions are not established.
When it helps
If access to ability levels 8 or 9 matters to your plan, the passage says multiclass characters cannot reach those levels in either class.
The tradeoff
The described multiclass schedule advances power levels less often than the single-class schedule and excludes the two highest ability levels in each selected class.
Read the supporting references
Check the edition and source version for patch-specific details. Guide methodology.