Marathon Digital, the world’s largest Bitcoin (BTC) miner by market cap, saw its shares rise 18% after it was confirmed to be joining the SP SmallCap 600 index fund.

The SP Dow Jones Indices said after trading on Friday, May 3 that Marathon would replace heating and ventilation manufacturing firm Aaon in the index on May 8.

The SP SmallCap 600 tracks 600 United States companies with a market cap between $1 billion and $6.7 billion posting profits both in the most recent quarter and the last four quarters.

On Monday May 6, Marathon Digital (MARA) shares rallied nearly 18% to $20.67, according to Google Finance.

Its stock price is up 25.2% since the April 20 Bitcoin halving which sliced miner block rewards from 6.25 BTC to 3.125 BTC, worth $198,000 at current prices.

However, MARA is down 9.86% year-to-date, it reached a 2024 high of $31.03 on Feb. 28.

Marathon is likely to be one of the larger-weighted stocks given its $5.6 million market cap and the SP SmallCap 600 using a float-adjusted market cap weighting method.

Marathon’s addition to the index comes as it is set to post its first-quarter earnings on May 9, which investment research firm Zacks expects  will see a 280% year-on-year (YOY) revenue increase to $193.9 million and $0.02 earnings per share — a 166.7% YOY jump.

Related: Marathon Digital, Kenyan government discuss crypto policy, energy use

Shares of Marathon’s rival Bitcoin mining firms also performed well on May 6 with CleanSpark (CLSK) and TeraWulf (WULF) seeing respective jumps of nearly 8% and 10.7%.

Change in share prices of the top eight largest Bitcoin mining firms on May 6. Source: Companies Market Cap

The rise in Bitcoin mining stocks comes amid a decrease in miner revenue due to the impact of the halving.

Transaction fees were consistently above 3.125 BTC for the first few hundred blocks post-halving, effectively offsetting the newly halved block subsidy.

However, transaction fees have since fallen and are now hovering around 0.2 BTC to 1 BTC at block 842,350, according to mempool.space data.

Magazine: 68% of Runes are in the red — Are they really an upgrade for Bitcoin?