Starting year
2409
Star Trek Online's current official story page sets the normal 25th-century starting point in 2409.
Star Trek Online · Answers · Timeline ·
-PTF- Answers
When does Star Trek Online take place?
Star Trek Online's main storyline is set in the early 25th century. It starts in 2409 and later story material reaches 2412. STO also uses time travel and alternate-era character starts, so some missions take place outside that range.
Direct Answer
Main STO storyline: 2409 → 2412
Later storyline
2412
The STO Wiki chronology extends the in-game timeline through 2412, with Axiom and the events following it placed in that year.
Context
Why do other years appear in STO?
Main timeline
2409–2412 is the core 25th-century story range.
The story advances through 2409, 2410, 2411 and 2412 rather than staying fixed in its original starting year.
Full reference: STO Wiki — Chronology (opens in new tab)