PIMCO has the largest share of the active ETF market by far. With $7.86 billion in assets, PIMCO holds almost half of market share according to AdvisorShares Investments as of June 20.

While active ETFs are gaining ground, they still make up just a small fraction of the ETF space and PIMCO has yet to break into the top 10 providers of ETFs overall.

However, PIMCO's recent shift in management with El-Erian's departure may disturb its large share of the active ETF space. "I think that whatever challenges they face in the mutual fund space will basically spill over into the ETF space," says Aniket Ullal, founder of First Bridge Data, a provider of ETF data and analytics.

Noah Hamman, the chief executive officer of active ETF provider AdvisorShares, adds: "Couple PIMCO's presence with additional more established mutual fund firms such as Doubleline, and Legg Mason, announcing plans to develop actively managed ETFs, we could see much more balanced offering of active ETF sponsors than the big three firms that dominate the index ETF space."

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