ESS Tech, Inc., a manufacturer of long-duration energy storage systems, has been officially added to the Russell Microcap Index. The change became effective after the US market close on June 27th as part of the FTSE Russell's annual index reconstitution.

The Russell Microcap Index primarily tracks the performance of the micro-cap segment of the US equity market, representing approximately the smallest 2% of the total US stock market capitalization. It comprises the smallest 1,000 securities in the Russell 2000 Index plus the next smallest 1,000 eligible securities by market capitalization. As of June 30, 2025, the index had an average market cap of $722 million and a median market cap of $243 million.

ESS Tech, Inc. is headquartered in Wilsonville, Oregon, and focuses on designing and manufacturing iron flow battery long-duration energy storage systems for commercial and utility-scale applications. The company has recently made several business advances, including collaborating with Salt River Project and Google on the Project New Horizon initiative to deploy a 5 MW / 50 MWh system in Arizona, and securing a $9.9 million contract from the US Air Force Research Laboratory. For the first quarter of this year, the company reported revenue of $128,000 and a narrowed net loss of $15.9 million, with adjusted EBITDA loss improving by 31% year-over-year.

Inclusion in the Russell Microcap Index is expected to enhance ESS Tech's visibility within the investment community, particularly attracting attention from passive funds and institutional investors that track the index. ESS Tech has now been included in the index for four consecutive quarters, reflecting its stability as a representative component of the micro-cap segment. As of the end of the first quarter of 2026, the company held approximately $15.5 million in cash and cash equivalents and $6 million in short-term investments.