Menlo Ventures is partnering with Fireworks in its **$1.5 billion Series D**. Fireworks is building a platform for specialized intelligence and low-cost token production, addressing a market that came into sharp focus in **2026**, when models gained the ability to sustain long-running tasks. Open-source usage on OpenRouter has expanded **more than 10x since the start of the year**. Fireworks’ daily token volume has **nearly tripled since late last year, from 15 trillion to 43 trillion**, while annualized revenue recently reached **$1 billion**. The platform integrates continued pretraining, supervised fine-tuning, and reinforcement learning with inference, using its proprietary FireAttention stack to automate configuration across hardware, quantization, sharding, speculative decoding, batching, and kernels. Customers include Cursor, which trained **Composer 2** on the platform, and Vercel, which delivered **40x improvements in latency** to v0 users by partnering with Fireworks on reinforcement learning.