libwebp 0.6.0 was tagged on Monday as the newest version of this WebP library. WebP 0.6 brings lossless performance and compression improvements, various performance improvements for SSE2 / NEON / MSA, the webpmux command gained a duration option, and there's a new img2webp utility.
The img2webp utility is designed for converting a sequence of images into an animated WebP file.
The libwebp 0.6 release does come with a few API changes. Libwebp 0.6.0 can be downloaded from the WebP project site.