It carries three normally-open main contacts and zero normally-closed main contacts, so it is a straightforward three-pole make-only device for three-phase motors or resistive heaters. For AC-4 duty (plugging, inching, reversing of squirrel-cage motors), it is rated 15.5 A at 400 V, which is the more demanding switching cycle that wears contacts faster. The front face carries IP20 protection — safe for finger contact in a closed panel — while the terminals themselves are rated IP00, meaning they require enclosure protection against tool contact.
For a BOM freeze or long-term project, this contactor is a safe choice: the SIRIUS platform has broad installed base and Siemens typically supports these sizes for years. If you need a drop-in alternative for a panel originally specified around the 3RT1017-1AP01, note that the 3RT1026 is a larger frame (S0 vs the smaller S00 of the 3RT1017) — it will not fit the same DIN footprint without panel rework. The 3RT1026 carries higher current ratings, so it is an upgrade in capability but not a mechanical substitute.