# What Is the New-Author Boost? How X’s Algorithm Elevates Posts From Low-Impression Authors

> Discover the New-Author Boost on X. Learn how this algorithm feature gives emerging creators visibility by elevating low-impression posts on the home timeline.

- Repository: [SpaceXAI Org/x-algorithm](https://github.com/xai-org/x-algorithm)
- Tags: deep-dive
- Published: 2026-09-10

---

**The New-Author Boost is a ranking multiplier that elevates posts toward the top of X’s home timeline when the author has accumulated fewer than 100 cumulative impressions, ensuring emerging creators gain visibility alongside established accounts.**

The New-Author Boost operates within the `xai-org/x-algorithm` codebase as a fairness mechanism in the home-mixer pipeline. By detecting authors with low historical reach and applying a configurable score boost, the system prevents a "rich-get-richer" dynamic where only popular accounts dominate user feeds. This technical implementation examines author impression counts at query time and dynamically adjusts ranking scores before final placement.

## How the New-Author Boost Works

The boost operates through a staged pipeline that evaluates author history and adjusts ranking position accordingly.

### Impression Threshold Check

When the home-mixer evaluates a candidate post, it retrieves the author’s cumulative impression count from the query-level feature store. As defined in [`home-mixer/params/param.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/params/param.rs), the system compares this count against the **ColdStartImpressionThreshold** parameter (default: 100). Authors with impression counts below this threshold are classified as "new" and qualify for elevation.

### Score Multiplication and Position Capping

For qualifying posts, the raw ranking score undergoes two sequential adjustments:

1. **Multiplicative scaling** – The raw score is multiplied by **ColdStartImpressionScale** (default: 2.0), effectively doubling the post’s competitiveness in the ranking algorithm.
2. **Position constraint** – The **LowImpressionsMaxPositionRatio** parameter (default: 0.20) prevents over-elevation by capping the boosted post’s position to the top 20% of the feed length. This ensures new authors gain visibility without completely displacing high-quality content from established creators.

The [`home-mixer/scorers/author_cold_start.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/scorers/author_cold_start.rs) file implements this logic, calculating a `target_position` based on the feed length multiplied by the maximum position ratio, then inserting the candidate at the higher of its raw or boosted position.

## Configuration Parameters

The behavior of the New-Author Boost is controlled through three tunable parameters defined in the configuration layer:

```rust
// home-mixer/params/param.rs
param!(
    ColdStartImpressionThreshold,
    u64,
    "rust_home_mixer_cold_start_impression_threshold",
    100            // authors with < 100 impressions are “new”
);
param!(
    ColdStartImpressionScale,
    f64,
    "rust_home_mixer_cold_start_impression_scale",
    2.0            // boost factor applied to the raw score
);
param!(
    LowImpressionsMaxPositionRatio,
    f64,
    "rust_home_mixer_low_impressions_max_boost_position_ratio",
    0.20           // boosted posts cannot be placed beyond the top 20 % of the feed
);

```

These parameters allow X’s ranking engineers to tune sensitivity: lowering the threshold captures more authors, while increasing the scale factor provides stronger elevation to those who qualify.

## Implementation in author_cold_start.rs

The scoring implementation retrieves these parameters at query time and applies conditional logic to each candidate post:

```rust
// home-mixer/scorers/author_cold_start.rs
let impression_threshold = query.params.get(ColdStartImpressionThreshold) as u64;
let impression_scale = query.params.get(ColdStartImpressionScale);
let max_pos_ratio = query.params.get(LowImpressionsMaxPositionRatio);

// For each candidate post:
if let Some(imp) = author_impression_count {
    if imp < impression_threshold {
        // Apply the boost
        let boosted_score = raw_score * impression_scale;
        // Ensure the boosted position stays within the allowed ratio
        let target_position = (feed_len as f64 * max_pos_ratio).floor() as usize;
        // …insert the candidate at `target_position` in the ranking list…
    }
}

```

This code path executes during the home timeline’s scoring phase, ensuring that elevation decisions occur before final ranking consolidation.

## Telemetry and Monitoring

To ensure the New-Author Boost functions as intended without degrading feed quality, X’s pipeline logs all boosted posts to the telemetry metric `home_mixer.cold_started_posts_total`. This monitoring allows engineers to track how frequently the boost triggers, measure engagement rates on elevated content, and adjust the impression threshold or scale factors based on real-world performance data.

## Summary

- The **New-Author Boost** targets authors with fewer than 100 cumulative impressions, preventing established accounts from monopolizing the home timeline.
- Elevation occurs through **multiplicative score scaling** (default 2.0×) combined with a **position cap** (top 20% of feed) to balance visibility and quality.
- Configuration resides in [`home-mixer/params/param.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/params/param.rs), while the scoring logic lives in [`home-mixer/scorers/author_cold_start.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/scorers/author_cold_start.rs).
- Boosted posts are tracked via the `home_mixer.cold_started_posts_total` telemetry metric for ongoing optimization.

## Frequently Asked Questions

### What is the New-Author Boost in X’s algorithm?

The New-Author Boost is a ranking adjustment mechanism that identifies posts from creators with low historical visibility (fewer than 100 impressions) and elevates their position in the home timeline. It applies a multiplicative score boost and position cap to ensure emerging voices receive algorithmic promotion without overwhelming the feed.

### How does the algorithm prevent new-author posts from completely dominating the feed?

The system enforces the **LowImpressionsMaxPositionRatio** parameter (default 0.20), which restricts boosted posts to the top 20% of the timeline regardless of their raw score. This cap ensures that while new authors gain visibility, they cannot displace all high-quality content from established creators.

### Where can I find the source code for the New-Author Boost?

The implementation resides in two primary files within the `xai-org/x-algorithm` repository: [`home-mixer/scorers/author_cold_start.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/scorers/author_cold_start.rs) contains the scoring logic, while [`home-mixer/params/param.rs`](https://github.com/xai-org/x-algorithm/blob/main/home-mixer/params/param.rs) defines the configurable parameters including the impression threshold and scale factor.

### How does X measure the effectiveness of the New-Author Boost?

All posts receiving the boost are logged to the `home_mixer.cold_started_posts_total` telemetry metric. Engineers monitor this data alongside engagement metrics to ensure the boost surfaces quality content from new creators rather than simply promoting low-value posts, allowing for data-driven adjustments to the threshold and scale parameters.