MODEL ID runware:ace-step@v1.5-xl-base

coming-soon

ACE-Step v1.5 XL Base

April 2, 2026

ACE-Step v1.5 XL Base is the 4B DiT variant of ACE-Step 1.5 for high-quality music generation and editing. It supports text-to-music, cover generation, repaint, extract, lego, and complete workflows, uses 50 inference steps with CFG, and is designed for longer-form audio generation up to 10 minutes with broad multilingual prompt support.

API Options

Platform-level options for task execution and delivery.

taskType string required value: audioInference: Identifier for the type of task being performed

taskUUID string required UUID v4: UUID v4 identifier for tracking tasks and matching async responses. Must be unique per task.

outputType string default: URL: Audio output type.

Allowed values 3 values

outputFormat string default: MP3

Specifies the file format of the generated output. The available values depend on the task type and the specific model's capabilities.

`MP3`: Compressed audio, smaller file size.
`WAV`: Uncompressed, high-quality audio.
`FLAC`: Lossless compression.
`OGG`: Open-source compressed audio format (Vorbis codec).

Allowed values 4 values

audioSettings object

Audio encoding settings for controlling the bitrate, number of channels, and sample rate of the generated audio. Only applicable for lossy output formats (MP3 and OGG). When using lossless formats (WAV or FLAC), this parameter must not be provided.

The available sample rates and valid bitrate ranges depend on the output format. For OGG, bitrate limits also vary by the number of channels.

MP3 bitrate limits

Bitrate limits for MP3 are the same regardless of mono or stereo.

Sample Rate	Min Bitrate	Max Bitrate
8,000 Hz	8 kbps	64 kbps
11,025 Hz	8 kbps	64 kbps
12,000 Hz	8 kbps	64 kbps
16,000 Hz	8 kbps	160 kbps
22,050 Hz	8 kbps	160 kbps
24,000 Hz	8 kbps	160 kbps
32,000 Hz	32 kbps	320 kbps
44,100 Hz	32 kbps	320 kbps
48,000 Hz	32 kbps	320 kbps

OGG bitrate limits — Mono (1 channel)

Sample Rate	Min Bitrate	Max Bitrate
8,000 Hz	8 kbps	40 kbps
12,000 Hz	16 kbps	48 kbps
16,000 Hz	16 kbps	96 kbps
24,000 Hz	16 kbps	80 kbps
48,000 Hz	32 kbps	224 kbps

OGG bitrate limits — Stereo (2 channels)

Sample Rate	Min Bitrate	Max Bitrate
8,000 Hz	16 kbps	80 kbps
12,000 Hz	16 kbps	96 kbps
16,000 Hz	24 kbps	192 kbps
24,000 Hz	32 kbps	160 kbps
48,000 Hz	48 kbps	256 kbps

Lossless formats: When outputFormat is set to WAV or FLAC, the audioSettings parameter is not available since these formats produce uncompressed or lossless audio with no configurable encoding settings.

Properties 3 properties

audioSettings » bitrate bitrate integer min: 8: Audio bitrate in kbps.

audioSettings » channels channels integer default: 2: Number of audio channels. 1 for mono, 2 for stereo.

Allowed values 2 values

audioSettings » sampleRate sampleRate integer: Audio sample rate in Hz.

webhookURL string URI

Specifies a webhook URL where JSON responses will be sent via HTTP POST when generation tasks complete. For batch requests with multiple results, each completed item triggers a separate webhook call as it becomes available.

Learn more 1 resource

Webhooks
PLATFORM

deliveryMethod string default: sync

Determines how the API delivers task results.

Allowed values 2 values

: Returns complete results directly in the API response.
: Returns an immediate acknowledgment with the task UUID. Poll for results using getResponse.

Learn more 1 resource

Task Polling
PLATFORM

uploadEndpoint string URI

Specifies a URL where the generated content will be automatically uploaded using the HTTP PUT method. The raw binary data of the media file is sent directly as the request body. For secure uploads to cloud storage, use presigned URLs that include temporary authentication credentials.

Common use cases:

Cloud storage: Upload directly to S3 buckets, Google Cloud Storage, or Azure Blob Storage using presigned URLs.
CDN integration: Upload to content delivery networks for immediate distribution.

// S3 presigned URL for secure upload
https://your-bucket.s3.amazonaws.com/generated/content.mp4?X-Amz-Signature=abc123&X-Amz-Expires=3600

// Google Cloud Storage presigned URL
https://storage.googleapis.com/your-bucket/content.jpg?X-Goog-Signature=xyz789

// Custom storage endpoint
https://storage.example.com/uploads/generated-image.jpg

The content data will be sent as the request body to the specified URL when generation is complete.

ttl integer min: 60: Time-to-live (TTL) in seconds for generated content. Only applies when outputType is URL.

includeCost boolean default: false: Include task cost in the response.

numberResults integer min: 1 max: 4 default: 1: Number of results to generate. Each result uses a different seed, producing variations of the same parameters.

Inputs

Input resources for the task (images, audio, etc). These must be nested inside the inputs object.

inputs » audio audio string: Audio input (UUID or URL).

Core Parameters

Primary parameters that define the task output.

model string required value: runware:ace-step@v1.5-xl-base: Identifier of the model to use for generation.

positivePrompt string required min: 2 max: 3000: Text prompt describing elements to include in the generated output.

negativePrompt string min: 2 max: 3000: Prompt to guide what to exclude from generation. Ignored when guidance is disabled (CFGScale ≤ 1).

duration float min: 30 max: 300 step: 0.1 default: 60: Length of the generated audio track in seconds.

seed integer min: 0 max: 2147483647: Random seed for reproducible generation. When not provided, a random seed is generated in the unsigned 32-bit range.

steps integer min: 1 max: 300 default: 100: Total number of denoising steps. Higher values generally produce more detailed results but take longer.

CFGScale float min: 1 max: 30 step: 0.01 default: 10: Guidance scale representing how closely the output will resemble the prompt. Higher values produce results more aligned with the prompt.

strength float min: 0 max: 1 step: 0.01 default: 0.5: Fraction of steps using the input source instead of generated output.

Settings

Technical parameters to fine-tune the inference process. These must be nested inside the settings object.

settings » bpm bpm integer min: 30 max: 300: Beats per minute. If not set, the model decides automatically.

settings » cfgIntervalEnd cfgIntervalEnd float min: 0 max: 1 step: 0.01 default: 1: Diffusion ratio where CFG ends (1.0 = last step).

settings » cfgIntervalStart cfgIntervalStart float min: 0 max: 1 step: 0.01 default: 0: Diffusion ratio where CFG begins (0.0 = first step).

settings » coverConditioningScale coverConditioningScale float min: 0 max: 1 step: 0.01 default: 1: Fraction of denoising steps using source-audio conditioning. Only effective when input audio is provided. 1.0 uses source conditioning for all steps.

settings » guidanceType guidanceType string default: apg

Controls how guidance is applied during generation.

Allowed values 2 values

: Adaptive Projected Guidance.
: Classifier-Free Guidance.

settings » keyScale keyScale string: Musical key and scale in '{Note}{Accidental} {Mode}' format (e.g. 'C major', 'F# minor', 'Bb major').

settings » lyrics lyrics string min: 10 max: 3000: Song lyrics, typically formatted like a lyrics website.

settings » repaintingEnd repaintingEnd float min: 0 max: 300: End time in seconds for repaint region. Requires input audio. Values beyond audio duration append new audio.

settings » repaintingStart repaintingStart float min: -300 max: 300: Start time in seconds for repaint region. Requires input audio. Negative values prepend audio before the start.

settings » timeSignature timeSignature integer: Beats per measure. If not set, the model decides automatically.

Allowed values 4 values

settings » vocalLanguage vocalLanguage string default: en: ISO 639-1 language code for vocals. unknown for instrumental or auto detection.

Allowed values 51 values

Features

Standalone addons and post-processing features.

advancedFeatures » modularScheduler modularScheduler object: Manual scheduler configuration for fine-grained control over the diffusion process (sampler, modifiers, etc.).