minimal:
reqprocessor: 2 GHz, SSE2 support
reqgraphics: OpenGL 2.1-compatible, 512 MB video memory, framebuffer object support. E.g. Intel HD 4600 or better.
reqmemory: 1024 MB RAM
reqdiskspace: 320 MB available space
reqsystem: Steam OS 2.0 / Ubuntu 14.04 LTS
reqother: You may need to update your graphics drivers for OpenGL 2.1 support.

recommended:
reqprocessor: 2 GHz dual-core
reqgraphics: Geforce GTX 660 / Radeon 7870 or better.