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This is the draft that ultimately became https://medium.com/@filoz/the-f3-journey-f3-comes-to-mainnet-launch-date-and-preparation-guide-2addc240aaf2

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After a long time of research, implementation work, and rigorous testing, we're thrilled to announce that Fast Finality (F3) is being activated on the Filecoin Mainnet! This milestone represents the culmination of a long journey that began with theoretical research on consensus mechanisms, progressed through complex protocol design, survived countless whiteboard sessions and developer hours with final parameters emerging from extensive passive testing (nv24, nv25). It will soon will become a reality that will transform and speed up the Filecoin network!

F3's story began with early research into how faster finality could be brought to Filecoin's unique architecture. The first research papers and proof of concept were created by the ConsensusLab team, and then followed by the technical specifications and implementations, to the recent extensive passive testing at 100% network scale. Each step has built upon the last to create a solution that delivers on the promise of a faster, more reliable transaction finality in Filecoin.

What once seemed like a distant goal is now mere days away from becoming an integral part of the network. This isn't just a technical upgrade; adding another consensus mechanism to the Filecoin network will empower builders, improve user experiences, and strengthen Filecoin's position as a cutting-edge decentralized storage infrastructure.

🗓️ Mark Your Calendars: F3 Launch Date

🚀 F3 will be activated on the Filecoin mainnet on 2025-04-29 at 10:00 UTC (epoch 4920480) 🚀

The F3 activation on Mainnet follows the successful deployment of network version 25 on April 14th and comes after extensive passive testing that has consistently demonstrated F3's readiness for mainnet.

After 17 rounds of passive testing after nv25 activated, we have identified four F3 parameter adjustments that played a key role in network stability and performance, which we have adjusted accordingly:

• QualityDeltaMultiplier: increased from 1 to 8
  • The QualityDeltaMultiplier extends the QUALITY phase timeout to facilitate better propagation of proposals across the network, while keeping the timeout for other phases unaffected to maintain fast and consistent progress towards finalization.
• Internal pub-sub channel buffer sizes: the internal buffer sizes for queueing the pub-sub messages prior to processing were increased significantly to eliminate dropping messages before they get to be processed.
  • This helped address a message processing bottleneck, caused by slow calls to fetch the chain state as part of message validation and instance start. Additionally, all F3 messages are processed sequentially to guarantee a consistent state. The increase in buffer size allows for a larger number of messages to be queued up before being processed, which helps to ensure that messages are not dropped and that the system can keep up with the incoming message rate.
• MaxChainLength: reduced from 100 to 20.
  • The longer the chain, the more state needs to be fetched and validated, which can lead to performance issues considering the slow response time of interacting with the chain state. The MaxChainLength parameter is used to limit the number of tipsets that are picked for each F3 finalization round. By reducing this value, we can reduce the amount of state that needs to be fetched and validated, which can help to improve performance and further aid F3 to keep up with the rate of incoming messages.
• HeadLookback: set to 4.
  • By setting this value to 4, we can ensure that F3 is able to finalize blocks that are at least 4 blocks behind the chain head. This contributes to the correctness of F3 in terms of design goals: graceful co-existence with the EC chain.

As we shared our blog post Delegated Authority for Faster Mainnet Activation of F3, we're able to accelerate the activation timeline on Mainnet thanks to the delegated authority mechanism that allowed us to fine-tune parameters and set these parameters through a contract without waiting for an additional network upgrade. (You can follow the activation steps here.)

🔍 What to Expect When F3 gets activated

First of all there are two phases to be aware of when F3 gets activated on 2025-04-29 at 10:00 UTC.

1. The Bootstrap Phase: Where F3 catches up to the latest state
2. The Steady State Phase: The ongoing finalization of the chain after the initial Bootstrap phase