4 Signs the Altcoin Season Is Accelerating in September

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The altcoin market is approaching its all-time high capitalization, just a few percentage points away from the record. Many analysts suggest that September could mark the acceleration phase of the “altcoin season” — the cycle in which altcoins outperform Bitcoin. Below are four key signals being closely monitored by market observers.

1. Altcoin Trading Volume Surpasses Bitcoin and Ethereum

This trend reflects a familiar capital rotation pattern: starting with Bitcoin, moving to Ethereum, and eventually flowing into altcoins, thereby fueling the altseason. The drop in Ethereum’s share also aligns with this cycle.

2. Altcoin Season Index Reaches 2025 High

The Altcoin Season Index (ASI) from Blockchain Center climbed to 80 points — its highest level in 2025. ASI measures the performance of the top 50 cryptocurrencies (excluding stablecoins) against Bitcoin over the past 90 days. With 75% of altcoins outperforming BTC, the data confirms that the market is firmly in altcoin season.
Analyst Lau noted that the acceleration phase of altcoin season can last anywhere from 17 to 117 days, depending on market dynamics.

3. Altcoin Market Cap (TOTAL3) Forms a Major Bullish Pattern

From a technical perspective, the TOTAL3 index — representing the total altcoin market capitalization excluding BTC and ETH — has been forming a bullish triangle for the past four years. It is now approaching its all-time high of $1.16 trillion.
Breaking above this level could trigger a new growth cycle for altcoins, as there are no historical resistance levels to reference. This is considered one of the most significant structural signals in the market today.

4. Major Exchanges Ramp Up Altcoin Listings

Alongside rising liquidity, several major exchanges have increased their altcoin listings in September. Upbit has been adding nearly one token per day, while Bithumb and Coinbase have also expanded their offerings with a wide range of new projects.
These listings enhance liquidity, attract investors, and increase trading activity, creating a feedback loop that further strengthens the altseason momentum.

Taken together, these signals suggest that the altcoin market is entering a strong growth phase. If the trend continues, September could become a pivotal moment in the 2025 altcoin season.

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