Teenage Engineering has released OS 2.5 for its $329 EP-133 KO II sampler, one of the biggest firmware updates yet for the pocket-sized device. The free update adds audio over USB, selectable lo-fi sample rates, sample reverse, an arpeggiator and more — and it doubles the maximum sample length, meaningfully widening what the compact sampler can do.
What's new in KO II OS 2.5
The headline additions reshape how the KO II handles samples and loops. The update extends the maximum sample length from 20 to 40 seconds by capturing in mono rather than stereo, and pairs that with equal-length autochopping. That makes the sampler far better suited to slicing and rearranging melodic loops — not just isolating drum hits the way the older transient-based chopper did. The full feature list includes:
- Audio over USB for cleaner routing into a computer or interface.
- Selectable sample rates: standard 46kHz, a characterful 32kHz mode, or a crunchy, fully lo-fi 26kHz mode.
- Sample reverse — a simple but long-requested feature.
- An arpeggiator that suits the KO II's strong sample repitching.
- 40-second sampling (up from 20) plus equal-length autochopping.
- Improved time stretching, new scales, per-pad time shifting, and bug fixes.
The standout features for music makers
The selectable sample rate is the most expressive addition. The 32kHz mode adds subtle warmth and grit, while 26kHz pushes sounds into crunchy, distinctly digital lo-fi territory — useful for beats that want texture baked in rather than added later. The arpeggiator may look unusual on a sampler, but because the KO II sounds so good repitching samples, it becomes a fast route to a synthpop bassline or a moving melodic pattern from a single captured note.
Sample reverse, meanwhile, is the kind of basic tool whose absence was genuinely surprising. Taken together with the longer 40-second capture and equal-length autochopping, these tools make it far more practical to load in a full melodic phrase and rework it, rather than being limited to short percussive snippets.
Availability across the EP range
OS 2.5 is not limited to the KO II. It is also available for the device's reggae-themed sibling, the EP-40 Riddim, which receives the same set of features. The quirky EP-1320 Medieval sampler is finally getting an OS update too — but it receives only USB audio and nothing else from the new feature set. Owners can update their KO II, EP-40 Riddim or EP-1320 Medieval through Teenage Engineering's official update guides.
That uneven rollout, with the Medieval left out of most of the new capabilities, is a recurring sticking point for the lineup, and the reasoning behind it remains unclear. Still, for most owners the update is a substantial, no-cost upgrade.
Why a firmware update like this matters
Updates like OS 2.5 show how software can meaningfully extend hardware long after launch. Rather than nudging owners toward a replacement, Teenage Engineering is adding genuinely new creative capabilities to a device people already own. For a compact, affordable sampler, that kind of ongoing support is a real part of the value proposition and a point in its favor against pricier gear.
KO II OS 2.5 FAQs
How long can the KO II sample now?
OS 2.5 doubles the maximum sample length from 20 to 40 seconds by recording in mono instead of stereo.
Does the update cost anything?
No. OS 2.5 is a free firmware update applied through Teenage Engineering's update guides. For more on the gadgets and creative tools worth following, browse our latest reviews and gear coverage, or keep up with new releases on our news feed.
