AI training firm Fleet is in talks to secure a new funding round of at least $50 million, aiming for a post-money valuation of approximately $750 million. This marks a significant increase from its initial seed round valuation of under $100 million. Bain Capital Ventures is leading the negotiations, with participation from Sequoia Capital, Menlo Ventures, and SV Angel.Founded in 2024, Fleet specializes in creating reinforcement learning training environments for AI labs, replicating popular applications like Salesforce and Excel. The company has experienced explosive growth, with annualized revenue soaring from $1 million to over $60 million recently. However, the sustainability of this growth is uncertain as AI labs may consolidate their data spending, impacting startups like Fleet.