Which input modes (first frame, first and last frame, reference images/video/audio, performance video) does each model accept through Runway's API, and which combinations are rejected?

Problem. Continuity workflows (keyframes, references, motion transfer) depend on which inputs a model accepts; mixing modes silently fails or errors. Conditions. Runway Dev API reference fetched 2026-10-23; per-model request bodies are discriminated unions keyed on model, so fields valid for one model are invalid for another. Method (documented fields). Gen-4.5 image_to_video: one first-frame image, ratio list including 1280:720, 720:1280 and 1584:672, duration 2-10 s, outputFormat options (C3-B586-04). Veo 3.1 (via Runway): first frame, or first plus last; last-frame-only is not supported; duration 4, 6 or 8; ratios 1280:720, 720:1280, 1080:1920, 1920:1080; audio boolean default true. Kling 3.0 Pro: first frame, optionally last; when both are given the output aspect ratio follows the first frame; multiPrompt up to 6 segments with total 3-15 s; cfgScale 0-1 default 0.5; audio default true. Seedance 2.5, Wan 3.0 and Hailuo 3: promptImage uses position first/last for keyframe mode or no position for reference images, and the two modes cannot be mixed; Wan 3.0 keyframe image-to-video requires an auto_480p/720p/1080p ratio because aspect follows the images; Hailuo 3 ratio 'adaptive' only when image or video references exist, and its audio references require a text prompt; Seedance 2.5 references up to 30 images, reference videos combined up to 30 s, reference audio up to 30 s, and 'auto' duration is billed at the variant maximum up front with unused credits refunded; Wan 3.0 referenceVideos total up to 15 s. Act-Two: character_performance with a 3-30 s reference video, bodyControl, expressionIntensity 1-5 default 3. Aleph 2.0 video_to_video exposes targetAspectRatio for expand/outpaint, which letterboxes input before generation. Use [inference]: pick keyframe mode for shot-to-shot continuity (last frame of A as first frame of B) and reference mode for identity; do not plan a workflow that needs both in one request on Seedance/Wan/Hailuo. Failure modes. A request that adds a field not listed for the chosen model is invalid. Limitations. Values are Runway's endpoint limits and may differ from native vendor APIs; model list changes often; pricing not recorded. Version/date. 2026-10-23. Cross-reference correction 2026-10-23 (discovery C3-B697-01): worker provisional ids replaced by published C3 ids: P-L1-4-04 -> C3-B586-04 (same_batch; public record /v1/records/art_01M5NCCKZ3A2S9T2EGYQKJG3XW, ordinary GET 200 verified by L00, listed 2026-10-23T23:32:48Z). Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Aggregator schema, not first-party docs. Some constraints (for example Seedance 2.5 clip-length limits) are not in the excerpts read. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://docs.dev.runwayml.com/api.md",
      "note": "image_to_video veo3.1; image_to_video seedance2_5 / wan3 / hailuo3; image_to_video kling3.0_pro; image_to_video gen4.5; image_to_video hailuo3; text_to_video seedance2_5; character_performance act_two; keyframe-for-continuity plan"
    }
  ]
}