Claude Opus 5.5 vs Muse Spark 1.3
Full profiles: Claude Opus 5.5 (Anthropic) and Muse Spark 1.3 (Meta): every benchmark, price and rank.
Updated · Data from 13 sources
As of 9 Nov 2026, Claude Opus 5.5 is ahead of Muse Spark 1.3 on quality (68.9 vs 61.7 on the BenchLeader Index), but Muse Spark 1.3 is 4.0× cheaper at $2.00 vs $8.00 per 1M tokens blended. Choose Claude Opus 5.5 for coding (80 vs 61), knowledge (74 vs 57), and reasoning (72 vs 60); choose Muse Spark 1.3 for fast first answers (36.1 s vs 380.6 s) and agents & tools (66 vs 63).
Key facts (as of 9 Nov 2026)
- Claude Opus 5.5 scores 68.9 on the BenchLeader Index and Muse Spark 1.3 scores 61.7 (BenchLeader, 9 Nov 2026).
- Claude Opus 5.5 costs $8.00 per 1M tokens blended (list price, 9 Nov 2026).
- Muse Spark 1.3 costs $2.00 per 1M tokens blended (list price, 9 Nov 2026).
- Of the 35 benchmarks both models have, Claude Opus 5.5 leads 32 (BenchLeader, 9 Nov 2026).
- On Arena WebDev, Claude Opus 5.5 is rated 1818 and Muse Spark 1.3 1654 (LMArena, as published by 9 Nov 2026).
Which to pick for…
The pick's numbers come first. Category scores on the BenchLeader scale (50 is the average model, 15 points one standard deviation). High confidence means a lead of half a standard deviation or more; under one point is called either.
| Use case | Pick | Why | Confidence |
|---|---|---|---|
| Coding | Claude Opus 5.5 | 80 vs 61 category score; Arena WebDev 1818 vs 1654 | High |
| Agents & tool use | Muse Spark 1.3 | 66 vs 63 category score; APEX-Agents 47.6% vs 73.5% | Medium |
| Maths | Claude Opus 5.5 | 74 vs 63 category score; FrontierMath Tiers 1–3 91.2% vs 74.0% | High |
| Reasoning | Claude Opus 5.5 | 72 vs 60 category score; HLE-Diamond (AA) 67.9% vs 33.7% | High |
| Knowledge | Claude Opus 5.5 | 74 vs 57 category score; AA-Omniscience v1.1 48.1 vs 22.4 | High |
| Long documents | Either | 67 vs 66 category score; AA-LCR v1.1 84.7% vs 83.0% | Either |
| Images and other media | Claude Opus 5.5 | 70 vs 66 category score; Code2Video-AA 1536 vs 1019 | Medium |
| Chat quality (human preference) | – | Only Muse Spark 1.3 has an Arena rating (69 category score) | Not comparable |
| Lowest cost | Muse Spark 1.3 | $2.00 vs $8.00 per 1M blended; agentic coding session $0.092 vs $0.320 | – |
| Fastest first answer | Muse Spark 1.3 | 36.1 s (Muse Spark 1.3 (max)) vs 380.6 s (Claude Opus 5.5 (max)) to the first answer token | – |
| High volume on a budget | Neither flagship | A smaller model is usually the better fit: Cheapest good LLMs, Fastest LLMs | – |
Key differences
- Claude Opus 5.5 (max) leads on quality: 68.9 vs 61.7.
- Claude Opus 5.5 (max) is stronger in coding, knowledge, long context, maths, multimodal, reasoning.
- Muse Spark 1.3 (max) is stronger in agents & tools, human preference.
- Muse Spark 1.3 (max) is 4.0× cheaper ($2.00 vs $8.00 per 1M blended).
At a glance
| Spec | Claude Opus 5.5 | Muse Spark 1.3 |
|---|---|---|
| Developer | Anthropic | Meta |
| Released | 22 Sep 2026 | 2 Sep 2026 |
| Context window (tokens) | 1,000,000 | 1,048,576 |
| Max output (tokens) | 128,000 (up to 300K on the Message Batches API (beta)) | – |
| Input types | text, image | – |
| Reasoning effort settings | low, medium, high, xhigh, max | – |
| Compared at | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) |
| Open weights | No | No |
| Price in / out / cached input per 1M | $4.00 / $20.00 / $0.200 | $1.25 / $4.25 / $0.150 |
| API model ID | claude-opus-5-5 | – |
| Where to use it | Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry | – |
Limits, availability and announced prices from the vendors' own pages: platform.claude.com (checked 20 Oct 2026). Everything else is from the day's data.
Category by category
Category scores on the BenchLeader scale: 50 is the average evaluated model, 15 points is one standard deviation. A gap under one point is called level.
| Category | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) | Leader |
|---|---|---|---|
| Reasoning | 72.3 | 59.8 | Claude Opus 5.5 |
| Coding | 80.4 | 60.7 | Claude Opus 5.5 |
| Agents & tools | 62.7 | 65.5 | Muse Spark 1.3 |
| Maths | 74.0 | 63.1 | Claude Opus 5.5 |
| Knowledge | 73.7 | 57.2 | Claude Opus 5.5 |
| Human preference | – | 69.0 | not comparable |
| Multimodal | 70.3 | 65.8 | Claude Opus 5.5 |
| Long context | 67.1 | 66.3 | level |
On one chart
Each domain on the index's own scale, where 50 is an average model. Click a domain to see the benchmarks behind it. Pick up to 5 models from the list.
Not drawn, measured for fewer than two of these models: Instruction following, Human preference.
Where sources disagree
Across the 35 benchmarks both have, Claude Opus 5.5 leads 32, Muse Spark 1.3 leads 3. Every overall index that rates both puts Claude Opus 5.5 ahead.
| Overall index | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) | Leader |
|---|---|---|---|
| BenchLeader Index | 68.9 | 61.7 | Claude Opus 5.5 |
| AA Intelligence Index v5.0 | 59.1 | 36.6 | Claude Opus 5.5 |
| Arena Text | 1506† | 1496 | Claude Opus 5.5 |
Each publisher runs its own tasks, harnesses and effort settings, so their overall verdicts can differ; BenchLeader reconciles them on one scale. † measured at another effort setting of the same model (the publisher did not test the one compared here).
Price, speed and latency
List prices blended at three input tokens per output token. Per-task prices use the token counts on the methodology page. Cost, tokens and time per benchmark task are measured: Artificial Analysis’ averages over its whole Intelligence Index run.
| Measure | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) |
|---|---|---|
| Blended price per 1M tokens | $8.00 | $2.00 |
| Input / output per 1M | $4.00 / $20.00 | $1.25 / $4.25 |
| Cached input per 1M | $0.200 | $0.150 |
| Price per task: chat reply | $0.0076 | $0.0018 |
| Price per task: summarize a 30-page report | $0.060 | $0.018 |
| Price per task: code edit | $0.054 | $0.014 |
| Price per task: agentic coding session | $0.320 | $0.092 |
| Price per task: structured extraction | $0.012 | $0.0034 |
| Agentic coding session, input mostly cached | $0.149 | $0.043 |
| Cost per benchmark task (AA Index) | $10.04 | $2.39 |
| Output tokens per task (AA Index) | 173k | 91k |
| Of which reasoning | 120k | 55k |
| Time per task (AA Index) | 25 min | 12 min |
| Output speed | 115 tok/s | 123 tok/s |
| Time to first answer | 380.6 s | 36.1 s |
| Time to a complete answer | 771.1 s | 88.3 s |
Per token is not per task: an average task of Artificial Analysis' Intelligence Index cost $10.04 on Claude Opus 5.5 (max) and $2.39 on Muse Spark 1.3 (max), and Claude Opus 5.5 (max) wrote 1.9× as many output tokens for the same work, which a per-token price hides.
Each model is compared at its best-ranked reasoning-effort setting. Claude Opus 5.5 (max) scores 68.9 and takes 381 s to its first answer token; Claude Opus 5.5 (xhigh) scores 65.5 in 84 s, Claude Opus 5.5 (high) scores 65.4 in 28 s. Muse Spark 1.3 (max) scores 61.7 and takes 36 s to its first answer token; Muse Spark 1.3 scores 59.2 in 4 s, Muse Spark 1.3 (xhigh) scores 58.1 in 13 s. Higher effort means more thinking before the answer: better scores, longer waits and more tokens billed. How reasoning effort changes scores and cost.
Every benchmark
140 benchmarks, grouped by category; each name links to the board and its leaders. † measured at another effort setting of the same model, shown for reference and not counted as a win.
| Metric | Publisher | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) |
|---|---|---|---|
| BenchLeader Index | BenchLeader | 68.9 | 61.7 |
| Agents & tools score | BenchLeader | 62.7 | 65.5 |
| Coding score | BenchLeader | 80.4 | 60.7 |
| Knowledge score | BenchLeader | 73.7 | 57.2 |
| Long context score | BenchLeader | 67.1 | 66.3 |
| Maths score | BenchLeader | 74.0 | 63.1 |
| Multimodal score | BenchLeader | 70.3 | 65.8 |
| Reasoning score | BenchLeader | 72.3 | 59.8 |
| Human preference score | BenchLeader | – | 69.0 |
| Blended price $/M | BenchLeader | $8.00 | $2.00 |
| Output speed | BenchLeader | 115 tok/s | 123 tok/s |
| Time to first answer | BenchLeader | 380.6 s | 36.1 s |
| Context window | BenchLeader | 1,000,000 tokens | 1,048,576 tokens |
| Reasoning | |||
| GPQA Diamond | Epoch AI Benchmarking Hub | 90.6% | – |
| Arena Hard Prompts | Arena (LMArena) | 1530† | 1515 |
| LiveBench 2.0 Reasoning | LiveBench | 92.2%† | 89.7%† |
| LiveBench 1.0 Reasoning | LiveBench | 92.2% | 89.7%† |
| GPQA Diamond (AA) | Artificial Analysis | – | 93.5% |
| Humanity's Last Exam (AA) | Artificial Analysis | 61.4% | 48.7% |
| HLE-Diamond (AA) | Artificial Analysis | 67.9% | 33.7% |
| ARC-AGI-1 | ARC Prize | 97.5% | – |
| ARC-AGI-2 | ARC Prize | 91.7% | – |
| CritPt | Artificial Analysis | 31.7% | 24.9% |
| CritPt v2 hard subset (AA) | Artificial Analysis | 68.0% | 48.0% |
| MysteryMechanism | Vals AI | 49.5%† | 36.0% |
| Chess Puzzles | Epoch AI Benchmarking Hub | 67.0% | 37.0% |
| Mystery Game Puzzles | Epoch AI Benchmarking Hub | 71.0% | 25.0% |
| LMCA | Epoch AI Benchmarking Hub | 68.2% | 53.9%† |
| DTBench | Epoch AI Benchmarking Hub | 98.9% | 96.5%† |
| BTF-3 | Epoch AI Benchmarking Hub | – | 14.1%† |
| Coding | |||
| SciCode | SciCode | 66.9% | 58.8% |
| FrontierCode | Cognition | 54.6%† | – |
| Arena Coding | Arena (LMArena) | 1546† | 1532 |
| Arena WebDev | Arena (LMArena) | 1818 | 1654 |
| LiveBench 2.0 Coding | LiveBench | 87.1%† | 83.1%† |
| LiveBench 1.0 Coding | LiveBench | 89.3% | 81.1%† |
| IOI | Vals AI | 95.1%† | 56.6% |
| Code Migration | Vals AI | 66.7%† | 47.4% |
Show all 140 benchmarks
| Metric | Publisher | Claude Opus 5.5 (max) | Muse Spark 1.3 (max) |
|---|---|---|---|
| Coding | |||
| Code Migration v1.1 | Vals AI | 81.0%† | – |
| ProgramBench | Vals AI | 18.5%† | 2.5% |
| SWE-bench Multimodal | Vals AI | 70.2%† | 43.1% |
| Vibe Code Bench 1-100 | Vals AI | 30.4%† | 20.5% |
| Vibe Code Bench v1.1 | Vals AI | 90.3%† | 85.9% |
| MirrorCode | Epoch AI Benchmarking Hub | 78.9%† | – |
| CursorBench | Cursor | 57.8% | 41.6% |
| ALE-Bench | Epoch AI Benchmarking Hub | 2147.4† | 1688.3† |
| FrontierSWE | Epoch AI Benchmarking Hub | 62.3% | 25.8% |
| Terminal-Bench 4.0 (AA) | Artificial Analysis | 59.6% | 33.3% |
| Terminal-Bench 2.1 (AA) | Artificial Analysis | – | 84.3% |
| Startrise Frontend | Startrise | 71.1%† | 74.7%† |
| GameBench 2 Overall | DuelLab GameBench 2 | 87.6† | 57.8† |
| GameBench 2 by reasoning setting | DuelLab GameBench 2 | 94.8† | 68.7† |
| Design Arena Website | Design Arena | 1325† | 1343 |
| FrontierCode 1.1 (AA) | Artificial Analysis | 52.2% | 40.6% |
| FrontierCode 2.0 (AA) | Artificial Analysis | 46.4% | 23.1% |
| Agents & tools | |||
| Terminal-Bench | Terminal-Bench | 65.8% | 14.8%† |
| Remote Labor Index | Scale AI / CAIS | 21.3%† | – |
| APEX-Agents | Mercor | 73.5% | 47.6% |
| Arena Agent | Arena (LMArena) | 20 | 2.2 |
| LiveBench Long Agentic | LiveBench | 72.8%† | 47.9%† |
| LiveBench Browser | LiveBench | 88.4%† | 30.9%† |
| LiveBench Agentic Coding | LiveBench | 71.7% | 64.1%† |
| Terminal-Bench 2.1 (Vals) | Vals AI | 87.6%† | 79.0% |
| MCP Atlas | Scale AI SEAL | 85.4%† | – |
| HiL-Bench | Scale AI SEAL | 59.0%† | 66.9%† |
| GDPval-AA v2.1, normalised score | Artificial Analysis | 68.3% | – |
| GDPval-AA v2.1 | Artificial Analysis | 1866 | – |
| τ³-Banking (AA) | Artificial Analysis | – | 50.5% |
| ITBench SRE (AA) | Artificial Analysis | 38.2% | 33.2% |
| Analyst Agent (AA) | Artificial Analysis | 56.3% | 37.5% |
| CUA-bench | Vals AI | 14.0% | 5.8% |
| CyberBench | Vals AI | 55.4%† | 72.7% |
| Finance Agent v2 | Vals AI | 58.6%† | 60.0% |
| Finance Agent v2.1 | Vals AI | 67.8%† | – |
| Harvey's Legal Agent Benchmark v1.1 | Vals AI | 9.2%† | – |
| Harvey's Legal Agent Benchmark v1 | Vals AI | 3.8%† | 23.8% |
| Legal Research Bench | Vals AI | 50.5%† | 55.3% |
| Robo-bench | Vals AI | 14.6% | – |
| SREBench | Vals AI | 33.6%† | 3.8% |
| Tax Agent Bench | Vals AI | 44.5%† | 42.4% |
| Terminal-Bench 4.0 (Vals) | Vals AI | 65.2%† | 24.8% |
| Terminal-Bench Science | Vals AI | 47.1%† | 10.0% |
| Time Horizon Index: KSP | Vals AI | 91.3%† | – |
| Arena Search | Arena (LMArena) | 1214† | – |
| Vending-Bench 2 | Andon Labs | 9235.3† | – |
| AutomationBench | Artificial Analysis | 69.5% | 57.9% |
| GDP.pdf (AA) | Artificial Analysis | 26.2% | 26.6% |
| Harvey LAB-AA v1.1 | Harvey | 4.2% | 8.9% |
| AA-Briefcase v1.1 | Artificial Analysis | 1800 | 1581 |
| GDPx | GDPx by SemiAnalysis | 12.0% | – |
| Design Arena Agentic | Design Arena | 1334† | 1278 |
| Terminal-Bench-Science 0.1 (AA) | Artificial Analysis | 59.0% | 10.9% |
| CWE-Bench (AA) | Artificial Analysis | 58.3% | – |
| DeepSec-Bench (AA) | Artificial Analysis | 26.9% | – |
| CyberGym end-to-end (AA) | Artificial Analysis | 0.8% | – |
| FACTS Search | 88.4%† | – | |
| Maths | |||
| FrontierMath Tiers 1–3 | Epoch AI Benchmarking Hub | 91.2% | 74.0% |
| FrontierMath Tier 4 | Epoch AI Benchmarking Hub | 95.0% | 46.3% |
| OTIS Mock AIME | Epoch AI Benchmarking Hub | 100.0% | 99.2%† |
| ProofBench | Vals AI | 100.0% | 58.0% |
| LiveBench Mathematics | LiveBench | 97.1% | 96.0%† |
| Arena Maths | Arena (LMArena) | 1518† | 1507 |
| Knowledge | |||
| SimpleQA Verified | Epoch AI Benchmarking Hub | 72.2% | – |
| LiveBench 2.0 Data Analysis | LiveBench | 80.3%† | 79.6%† |
| LiveBench Research | LiveBench | 88.9%† | 82.5%† |
| LiveBench 1.0 Data Analysis | LiveBench | 80.3% | 79.6%† |
| AA-Omniscience v1.1 | Artificial Analysis | 48.1 | 22.4 |
| PRBench Finance | Scale AI SEAL | – | 59.5%† |
| PRBench Legal | Scale AI SEAL | 47.6%† | 61.6%† |
| BioMysteryBench | Vals AI | 79.3%† | – |
| ClaimBench | Vals AI | 100.0%† | – |
| Excel Modeling Benchmark | Vals AI | 75.9%† | 67.4% |
| Excel Modeling Benchmark v1.1 | Vals AI | 75.8%† | – |
| MedCode | Vals AI | 49.8%† | – |
| MedScribe | Vals AI | 91.4%† | – |
| Public Benefits Bench v1.1 | Vals AI | 70.6%† | – |
| DrugDiscoveryBench | Scale AI SEAL | – | 62.2%† |
| EBR-bench | Epoch AI Benchmarking Hub | 71.4% | – |
| GDP.pdf | Epoch AI Benchmarking Hub | 30.6% | 27.6%† |
| AA-Omniscience v1.1: accuracy | Artificial Analysis | 65.5% | 38.0% |
| AA-Omniscience v1.1: non-hallucination | Artificial Analysis | 49.7% | 74.8% |
| HealthBench Professional (AA) | OpenAI | 59.9% | – |
| Instruction following | |||
| LiveBench Language | LiveBench | 86.3% | 82.8%† |
| LiveBench Instruction Following | LiveBench | 65.7% | 78.0%† |
| Arena Instruction Following | Arena (LMArena) | 1519† | 1485 |
| Human preference | |||
| Arena Text | Arena (LMArena) | 1506† | 1496 |
| EQ-Bench 4 | EQ-Bench | 1340† | – |
| Arena Creative Writing | Arena (LMArena) | 1517† | 1467 |
| Arena Multi-turn | Arena (LMArena) | 1500† | 1493 |
| Arena Longer Queries | Arena (LMArena) | 1520† | 1497 |
| Multimodal | |||
| Arena Vision | Arena (LMArena) | 1324† | 1309 |
| LiveBench Design | LiveBench | 83.3%† | 74.8%† |
| MMMU-Pro | Artificial Analysis | 87.7% | 82.0%† |
| SAGE | Vals AI | 91.3%† | – |
| Blueprint-Bench 2 | Epoch AI Benchmarking Hub | 51.2%† | – |
| Code2Video-AA | Artificial Analysis | 1536 | 1019 |
| AA-3D | Artificial Analysis | 1202 | 1032 |
| Long context | |||
| AA-LCR v1.1 | Artificial Analysis | 84.7% | 83.0% |
| Arena Document | Arena (LMArena) | – | 1475 |
| MLCR | Artificial Analysis | 27.8% | 13.9% |
| Composite | |||
| Epoch Capabilities Index | Epoch AI Benchmarking Hub | 168.4† | 158.0† |
| LiveBench 2.0 | LiveBench | 83.4%† | 68.4%† |
| LiveBench 1.0 | LiveBench | 83.2% | 81.6%† |
| AA Intelligence Index v5.0 | Artificial Analysis | 59.1 | 36.6 |
| AA Intelligence Index v4.3.2 | Artificial Analysis | 57.6 | 48.1 |
| AA Progress Index v1 | Artificial Analysis | 350 | 324.5 |
| Vals Index | Vals AI | 70.1† | – |
| Vals Finance Index | Vals AI | 65.3%† | – |
| Vals RSI Index | Vals AI | 37.3% | 19.6% |
| Vals Science Index | Vals AI | 58.6%† | – |
| Vals Router Index | Vals AI | 64.2%† | – |
| AA Cyber Index | Artificial Analysis | 28.7 | – |
| Safety & honesty | |||
| FORTRESS | Scale AI SEAL | 5.8% | – |
Data as of 2026-11-09. Best configuration of each model; every score links to its source on the model pages.
DuelLab GameBench 2, release gb2-20261103-eaea31df94e6 (https://benchmarks.duellab.org/releases/gb2-20261103-eaea31df94e6/), CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Scores mapped to BenchLeader model names; not endorsed by DuelLab.
What changed
- Claude Opus 5.5 (max): 2 score revisions.
- Claude Opus 5.5 (max): 1 score revision.
- Muse Spark 1.3 (max): 1 score revision.
- Claude Opus 5.5 (max): 1 score revision.
- Claude Opus 5.5 (max): 2 score revisions.
- Muse Spark 1.3 (max): 1 score revision.
- Claude Opus 5.5 (max): 2 score revisions.
- Claude Opus 5.5 (max): 1 score revision.
- Muse Spark 1.3 (max): 1 score revision.
- Muse Spark 1.3 (max): BenchLeader Index 64.5 → 61.8.
Related comparisons
- Claude Opus 5.5 vs Claude Fable 5.2
- Claude Opus 5.5 vs Gemini 4 Carbon
- Claude Opus 5.5 vs GPT-6 Astra
- Muse Spark 1.3 vs Claude Fable 5.2
- Muse Spark 1.3 vs Gemini 4 Carbon
- Muse Spark 1.3 vs GPT-6 Astra
- Claude Fable 5.1 vs Muse Spark 1.3
- Claude Opus 5.5 vs Muse Spark 1.2
Rankings: Best LLM overall · Best LLM for coding · Best LLM for agents · Best cheap LLMs
Claude Opus 5.5 vs Muse Spark 1.3: questions
- Is Claude Opus 5.5 better than Muse Spark 1.3?
- Claude Opus 5.5 (max) leads on quality: 68.9 vs 61.7. The BenchLeader Index combines every independent quality benchmark; Claude Opus 5.5 (max) is ahead overall as of 9 Nov 2026, but check the category scores for your use.
- Claude Opus 5.5 vs Muse Spark 1.3: which is cheaper, and will that change?
- Muse Spark 1.3 is cheaper today: $2.00 against $8.00 per million tokens, blended at three input tokens per output token. No price change has been announced for either.
- Is Claude Opus 5.5 or Muse Spark 1.3 better for coding?
- Claude Opus 5.5 scores higher in coding (80 vs 61 on the category index, where 50 is average). On Arena WebDev, the top shared coding benchmark, it is 1818 for Claude Opus 5.5 against 1654 for Muse Spark 1.3.
- Which is faster, Claude Opus 5.5 or Muse Spark 1.3?
- Muse Spark 1.3 streams faster (123 vs 115 output tokens per second, Artificial Analysis 7-day median).
- Is Claude Opus 5.5 or Muse Spark 1.3 better for agents and tool use?
- Muse Spark 1.3 scores higher in agentic tasks (66 vs 63 on the category index, where 50 is average). On APEX-Agents, the top shared agents & tools benchmark, it is 73.5% for Claude Opus 5.5 against 47.6% for Muse Spark 1.3.
More questions (4)
- Which is better for long documents?
- They are level on long-context benchmarks (67 vs 66). Both take about 1M tokens: Claude Opus 5.5 1,000,000, Muse Spark 1.3 1,048,576.
- Which has lower latency?
- Muse Spark 1.3 answers first: 36.1 s against 380.6 s to the first answer token, as Artificial Analysis measures it. Reasoning effort drives most of this: a higher setting thinks longer before it answers.
- Do independent benchmarks agree on Claude Opus 5.5 vs Muse Spark 1.3?
- Across the 35 benchmarks both have, Claude Opus 5.5 leads 32, Muse Spark 1.3 leads 3. Every overall index that rates both puts Claude Opus 5.5 ahead.
- When was Claude Opus 5.5 released?
- Claude Opus 5.5 was released on 22 Sep 2026.