claude-fable-5-1 vs step-5-preview
Parameters, independent leaderboard coverage, real-task reports and open-weight availability are shown side by side; missing coverage is not a zero.
Parameters
| Comparison item | claude-fable-5-1 | step-5-preview |
|---|---|---|
| Model Type | LLM | LLM |
| Context window | 1,000,000 tokens | — |
| Maximum output | 128,000 tokens | — |
| Input/output modalities | text, image → text | — |
| Endpoint | anthropic · openai | openai · anthropic · openai-response |
| Open weights | Unavailable | Unavailable |
| License | Proprietary hosted model | Not yet published |
Leaderboard coverage
Every independent board covering either model is retained; an em dash means that board has not published a figure for that model.
A row marked as retrieved on different dates holds two readings taken on different days; a board re-fits or changes version as a whole between readings, so those two figures are not directly comparable.
| Evaluation | claude-fable-5-1 | step-5-preview |
|---|---|---|
| LMArena Text Arena — Arena score (Elo) | 1501 ±6 | — |
| Artificial Analysis Intelligence Index — Intelligence Index | 53 | 44 |
| Epoch Capabilities Index (ECI) — General ECI | 165 (162 - 169) | — |
| LMArena Text Arena · Chinese — Arena score (Elo) | 1570 ±21 | — |
| LMArena Text Arena · Coding — Arena score (Elo) | 1531 ±13 | — |
| Artificial Analysis · Output Speed — Median output tokens/s | 65 | 83 |
| Artificial Analysis · GDPval-AA v2.1 — Agentic Real-World Work Tasks, (Elo-500)/2000 (%) | 62 | 53 |
| Artificial Analysis · Terminal-Bench v4.0 — Agentic Coding & Terminal Use (%) | 52 | 33 |
| Artificial Analysis · MLCR-AA — Medical Long Context Reasoning (%) Retrieved on different dates | 71.1 (retrieved 2026-09-07) | 16.7 (retrieved 2026-09-22) |
Real-task reports
claude-fable-5-1
- Step 5 Preview and Claude Fable 5.1 on one front-end prompt — Build a front-end page from a single prompt. Finding: Claude Fable 5.1 took 40 minutes and $17 on the front-end prompt that Step 5 Preview finished in 10 minutes for about $0.50; the author left the quality comparison to readers. Limitation: One prompt; the post leaves the quality comparison to readers rather than scoring it, and the cost gap follows each vendor's list prices.
- Cortex AI: GPT-6 Astra, Gemini 3.8 Flash and Fable 5.1 on two real robot tasks — Load a sandwich into a microwave and close the door; attach a 5 mm tip to a pipette. Finding: Fable 5.1 scored 6.7% on the microwave task and 20% on the pipette task, behind GPT-6 Astra (80% and 70%) and Gemini 3.8 Flash (13.3% and 30%). Limitation: The post does not say how many attempts each model had; scores are partial-credit judgements by the lab's evaluator, and the authors attribute the gap mainly to weaker depth perception in the lower-scoring models.
- AI Coding Daily LLM Coding Leaderboard — Implement and harden production-shaped projects in several stacks, including a Laravel app, a Go service and a React/TypeScript app, from the same prompts. Finding: Claude Fable 5.1 at medium reasoning scored 53.63 ($1.53 and 3 min 6 s per run in Claude Code), sixth of 47 rows, behind Claude Opus 5.5 and GPT-6 Astra. Limitation: One author's benchmark whose code-quality half is graded by a judge model; rows run in different harnesses, the page is updated as models are added (read on 2026-09-24, 47 rows), and the author sells premium tutorials and advertising.
step-5-preview
- Step 5 Preview and GPT-5.6 Sol on a Blender-to-3D-print task — Model an 8 cm spring caterpillar in Blender from a reference image, then 3D-print it. Finding: Step 5 Preview took 54 min 40 s against GPT-5.6 Sol's 14 min 34 s but gave the model a flat base that printed cleanly; Sol's version stood on a few small feet and nearly failed with stringing. Limitation: The author took part in StepFun's early evaluation. In a second round that spelled out printability in the prompt, both models did well, so the gap appeared only when the prompt left it implicit.
- Step 5 Preview and Claude Fable 5.1 on one front-end prompt — Build a front-end page from a single prompt. Finding: Step 5 Preview finished in 10 minutes for about $0.50; Claude Fable 5.1 took 40 minutes and $17. The repeated Step 5 run came out almost the same. Limitation: One prompt; the post leaves the quality comparison to readers rather than scoring it, and the cost gap follows each vendor's list prices.
- Step 5 Preview and DeepSeek V4.1 Flash on a 3D arcade game — Build Katamari Tiny, a 3D arcade game, from a single prompt. Finding: Step 5 Preview used 39,830 tokens against DeepSeek V4.1 Flash's 26,898, and the author judged DeepSeek's game faster and better. Limitation: One prompt judged by an author who names DeepSeek V4.1 Flash as their default model; the post gives no timings or quality rubric.
- Step 5 Preview and DeepSeek V4.1 Flash on one Three.js scene — A Three.js scene of giant red mesas in a desert, with long shadows and a huge empty sky. Finding: Step 5 Preview produced the richer scene, with better atmosphere, a tracked sun, more particle and dust effects and on-screen text; DeepSeek V4.1 Flash's version was more restrained but had clearly better ground and mesa textures and a smoother camera. Limitation: One prompt judged by eye by the author; the post does not say how either model was accessed.
- Step 5 Preview on the pelican-bicycle SVG — An HTML page with a 2D SVG animation of a pelican riding a bicycle. Finding: The scene looked good overall, roughly on a par with Kimi K3 in the author's view. Limitation: One prompt with a follow-up after a disconnection, judged by eye.
- Step 5 Preview on kzhu's six-question test — The author's six-question test: constrained sentences, pelican and compound-bow SVGs, a browser OS with a space game, a 3D racing game and a Trello board. Finding: Most sentences were fluent, the pelican and compound-bow SVGs were strong with only small detail issues, the browser OS was complete and its space game playable, the 3D racing game was refined, and the Trello board's interactions were smooth apart from one small UI flaw; the author rated the overall performance outstanding. Limitation: A summary without scores; Step 5 Preview does not appear on the author's leaderboard, so it cannot be compared with the scored rows.