Model comparison
Claude Fable 5.1 vs Upstage Solar Pro 4
Anthropic against Upstage, compared on context, price, and verified benchmark results.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: High — see receipts below
Anthropic
Claude Fable 5.1
Frontier
Upstage
Upstage Solar Pro 4
Frontier
| Specification | Claude Fable 5.1 | Upstage Solar Pro 4 |
|---|---|---|
| Provider | Anthropic | Upstage |
| Tier | Frontier | Frontier |
| Context window | Winner: 1M | 524K |
| Max output | 128K | Not verifiedUnverified |
| Input / 1M tokens | $10 | Winner: $0.30 |
| Output / 1M tokens | $50 | Winner: $1.20 |
| Weights | Closed | Closed |
| Parameters | Not disclosedUnverified | Not disclosedUnverified |
| Reasoning levels | adaptive | low, medium, high |
| Modalities | text, image | text |
| API model id | claude-fable-5-1 | solar-pro-4 |
| Released | September 1, 2026 | August 10, 2026 |
| Artificial Analysis Intelligence Index (2026-08-14) | Winner: 66 | 50 |
| Humanity's Last Exam (2026-09-01) | 65 | Not verifiedUnverified |
| Terminal-Bench 2.1 (2026-09-05) | 91.4 | Not verifiedUnverified |
| DeepSWE 1.1 (2026-09-03) | 67.4 | Not verifiedUnverified |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-09-05: Artificial Analysis Terminal-Bench v2.1 (independent, Terminus 2, max effort — current AA leader)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-09-03: OpenAI GPT-6 Astra launch chart (independent cross-vendor; Fable 5.1 not on the official Datacurve leaderboard)Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task. Comparability: directly comparable
- 2026-09-01: Anthropic announcement comparison table (vendor, with tools; 60.9 no tools)Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise. Comparability: comparable with caveat — Subset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.
- 2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
Pricing tiers: Claude Fable 5.1: Priced with Fable 5 at $10/$50 per MTok; cache reads cut 75% to $0.25/MTok. Adaptive thinking always on (default effort high); knowledge cutoff Jun 2026. Sibling Mythos 5.1 launched the same day. · Upstage Solar Pro 4: List $0.30/$1.20 per MTok; live promo rate is $0.03/$0.12 (90% off through 2026-09-10). Closed API. 524K context.
Claude Fable 5.1
Claude Fable 5.1 is Anthropic's September 2026 flagship refresh, debuting at the top of LiveBench and the Artificial Analysis Intelligence Index.
Best for
- Frontier agents
- Hardest reasoning work
- Fable 5 workloads at the same price
Watch out
Early-life model: leaderboard position is from launch-week boards; recheck before committing spend.
Upstage Solar Pro 4
Solar Pro 4 is Upstage's closed flagship with a 524K context at a low launch price.
Best for
- Long-context
- Cost-sensitive API
- Korean + English
Watch out
Closed API; promo pricing may end.
When the cheaper one wins
Upstage Solar Pro 4 is cheaper on output at $1.20 per million tokens against $50 for Claude Fable 5.1 — about 42×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: High
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 3/5 core specs verified on both sides — Not published for at least one side: max output, parameter count.
- 1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
- Verified within the last 90 days — Newest catalog check was 8 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- Claude Fable 5.1: Anthropic pricing — Fable 5.1/Mythos 5.1 $10/$50 (accessed 2026-09-03)
- Claude Fable 5.1: Anthropic models overview — Fable 5.1 (1M context, 128K output) (accessed 2026-09-03)
- Claude Fable 5.1: Artificial Analysis — Fable 5.1 Intelligence Index 66 #1 (accessed 2026-09-01)
- Upstage Solar Pro 4: Upstage — Solar Pro 4 (accessed 2026-08-29)
- Upstage Solar Pro 4: Upstage (accessed 2026-08-29)
Related comparisons
- Claude Fable 5.1 vs Claude Haiku 4.5
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs Claude Opus 5
- Claude Fable 5.1 vs Claude Sonnet 5
- Claude Fable 5.1 vs DeepSeek V4 Pro
- Claude Fable 5.1 vs Gemini 3.1 Pro
Diving deeper on one model? Claude Fable 5.1 · Upstage Solar Pro 4
Common questions
Claude Fable 5.1 vs Upstage Solar Pro 4
Answered from the verified figures on this page rather than general guidance.
Is Claude Fable 5.1 or Upstage Solar Pro 4 cheaper for input?
Upstage Solar Pro 4 is cheaper at $0.30 per million input tokens, against $10 for Claude Fable 5.1 — roughly 33× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Fable 5.1 has tiered pricing: Priced with Fable 5 at $10/$50 per MTok; cache reads cut 75% to $0.25/MTok. Adaptive thinking always on (default effort high); knowledge cutoff Jun 2026. Sibling Mythos 5.1 launched the same day. Upstage Solar Pro 4 has tiered pricing: List $0.30/$1.20 per MTok; live promo rate is $0.03/$0.12 (90% off through 2026-09-10). Closed API. 524K context.
Is Claude Fable 5.1 or Upstage Solar Pro 4 cheaper for output?
Upstage Solar Pro 4 is cheaper at $1.20 per million output tokens, against $50 for Claude Fable 5.1 — roughly 42× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Fable 5.1 has tiered pricing: Priced with Fable 5 at $10/$50 per MTok; cache reads cut 75% to $0.25/MTok. Adaptive thinking always on (default effort high); knowledge cutoff Jun 2026. Sibling Mythos 5.1 launched the same day. Upstage Solar Pro 4 has tiered pricing: List $0.30/$1.20 per MTok; live promo rate is $0.03/$0.12 (90% off through 2026-09-10). Closed API. 524K context.
Which has the larger context window, Claude Fable 5.1 or Upstage Solar Pro 4?
Claude Fable 5.1 accepts 1M tokens against 524K for Upstage Solar Pro 4. This only matters if you routinely send very long documents or large codebases.
Do Claude Fable 5.1 and Upstage Solar Pro 4 support the same reasoning levels?
Claude Fable 5.1 exposes adaptive, while Upstage Solar Pro 4 exposes low, medium, high.
Should I use Claude Fable 5.1 or Upstage Solar Pro 4?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Fable 5.1 suits frontier agents; Upstage Solar Pro 4 suits long-context.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: Upstage Solar Pro 4 costs $0.30 per 1M tokens versus $10 for Claude Fable 5.1 — a 33.3x difference at the headline tier.
- Context: Claude Fable 5.1 takes 1M against 524K for Upstage Solar Pro 4 — only decisive if your prompts approach the smaller window.
- Measured capability: Claude Fable 5.1 leads Artificial Analysis Intelligence Index 66 to 50 (measured 2026-08-14).
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.