# Phase 2: Multi-Builder PBS

### Proposer-Builder Separation — Brought to Solana

Once Phase 1's Open Orderflow Auction stabilizes, Phase 2 applies the battle-tested **PBS (Proposer-Builder Separation)** model from Ethereum to Solana, intensifying builder competition one step further.

***

### Multi-Builder Structure

We transition from a single builder (Flowra Builder) to a structure where **multiple external builders compete**.

| Builder Type     | Strategy                 | Characteristics                   |
| ---------------- | ------------------------ | --------------------------------- |
| **High Yield**   | MEV revenue maximization | Maximum tips, aggressive strategy |
| **No-Sandwich**  | User protection focused  | Sandwich attacks fully excluded   |
| **Low Variance** | Stable returns focused   | Minimal risk, predictable revenue |

Builders competitively submit block/bundle proposals based on the Open Orderflow stream, while the **Relay/Aggregator** layer collects and verifies them.

***

### Validator Policy Engine

The key innovation of Phase 2 is that validators no longer choose based solely on "highest tip" — they can **select builders aligned with their own policies and values**.

```
Selection criteria validators configure themselves:

  ✅ Revenue Maximization
  ✅ Toxicity Score (MEV quality)
  ✅ Risk & Compliance Score
  ✅ No-Sandwich Policy enforcement
  ✅ User protection options
```

Validators no longer need to follow Jito BAM's black-box decisions. By setting their own revenue, ethics, and risk criteria to select the optimal builder, they achieve **true Validator Sovereignty**.

***

### Phase 1 vs Phase 2

| Item                | Phase 1                | Phase 2                                |
| ------------------- | ---------------------- | -------------------------------------- |
| Builder             | Single Flowra builder  | Multiple external builders competing   |
| Builder selection   | Automatic              | Direct via Validator Policy Engine     |
| User protection     | Basic                  | Full No-Sandwich builder support       |
| Revenue competition | Searcher competition   | Dual competition: searchers + builders |
| Structure           | Open Orderflow Auction | Full PBS                               |


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