BARCELONA, SPAIN—We're live at Mobile World Congress, where Samsung is holding its "Unpacked 5" press event. The company has just announced its newest flagship smartphone, the Galaxy S5, and it says the new phone will launch in the US in April.

Samsung isn't really changing its formula with this new phone, which is very much in the mold of last year's Galaxy S4 and 2012's Galaxy S III. It's still a rounded rectangle made primarily of plastic, and it still has a removable plastic back that conceals a SIM slot and a removable battery. The phone is a little larger than the Galaxy S4, but not as large as a "phablet" like the Galaxy Note 3—leaked comparison shots show the S5 right in between the two. The phone still has a camera, LED flash, and speaker mounted on the back, but the micro-USB 2.0 port in the Galaxy S4 has been exchanged for the same larger, faster micro-USB 3.0 port used in the Note 3. The phone will be offered in black, blue, gold, and white, and more "designer colors" and patterns have been promised for the future. The phone's soft-touch plastic back has a "unique, perforated rear pattern" reminiscent of the 2012 Nexus 7. It should increase the phone's grippiness, a welcome improvement after a couple generations of slippery, smooth plastic.

As we expected from the new button layout of the Galaxy NotePro and TabPro, Samsung has finally ditched the legacy Android menu button in favor of the Google-recommended button set of Recent apps, Home, and Back. The buttons are still reversed compared to the standard layout used in Nexus phones—the Back button is to the right of the Home button and Recent Apps is on the left. Both of those are still capacitive buttons built in to the bottom bezel, while Home is a physical button that now integrates a fingerprint sensor. Just as with Apple's TouchID technology in the iPhone 5S, registered fingerprints can be used to unlock the phone and make mobile payments. Fingerprints are reportedly encrypted and stored locally.

The S5 is running Android 4.4.2, which is still being skinned with a version of Samsung's TouchWiz. The Settings menu appears to have been reorganized, presenting a grid of icons to tap instead of a list of settings to scroll through. A new Kids Mode will give younger users access to a few games or other apps, letting your kids play with Mom or Dad's phone without deleting all of the important data on it. We'll have to wait to get hands-on time with the phone to see what other tweaks Samsung has made to the software.

The phone has a 5.1-inch 1080p Super AMOLED display, slightly larger than last year's Galaxy S4. Samsung says the display can now be set to be "extremely dim" to prevent it from bothering those around you in the dark. It's also one of the first devices to use a Snapdragon 801 from Qualcomm. This "one louder" version of the Snapdragon 800 is architecturally identical, but it comes with faster CPU, GPU, and memory bus speeds, a bone Qualcomm has thrown to OEMs while it finishes up work on the true Snapdragon 800 successor, the 805.

The S5 also includes 2GB of RAM, 16 or 32GB of storage that can be expanded with up to 128GB of microSD storage, and a 2800 mAh battery. Samsung promises 10 hours of Web browsing on LTE and 12 hours of video playback on a single charge. It measures 142.0 x 72.5 x 8.1 mm and weighs 145 g, slightly larger and heavier than the Galaxy S4's 136.6 x 69.8 x 7.9 mm and 130 g. It is IP67 dust and water resistant, which should help prevent some damage from dust and dirt.

The new phone supports 802.11ac MIMO, which should allow for maximum transfer speeds of up to 867Mbps—many of last year's flagships included single-stream 802.11ac that was capped at 433Mbps. Category 4 LTE from Qualcomm allows LTE speeds of up to 150Mbps down and 50Mbps up, as long as your carrier supports them. Samsung says that its "download booster" technology can use Wi-Fi and LTE simultaneously to provide faster download speeds, though you'll want to be careful not to eat up your monthly data allotment by overusing the feature. Bluetooth 4.0 and NFC are also included, as is an IR blaster for use with television sets.

Like many other Galaxy phones, the S5 features compatibility with all of Samsung's wearable devices: the original Galaxy Gear, the new Tizen-based Gear 2 and Gear 2 Neo, and the new fitness-focused Gear Fit. The Galaxy S5 also includes some fitness hardware of its own—there's a heart rate sensor located next to the LED flash. Hold your finger over the sensor and it will track your current heart rate.

The S5 includes a 16MP rear camera with an LED flash and a 2.0MP front camera for video chatting. The camera features a hybrid autofocus lens and an improved image sensor. The rear camera promises 0.3 second autofocus times and "advanced HDR" capabilities, as well as a new Selective Focus feature that can simulate a lens with a shallow depth-of-field. Samsung says the phone's camera interface has also been revamped.

We'll be going hands-on with the phone and putting up more photos and impressions soon. Stay tuned!