Claude Opus 5 changelog

Arena text leaderboard: Gemini 4 Argon first, Opus 5.5 second, GPT-6 Astra 73rd

Arena's October 20, 2026 text leaderboard ranks Gemini 4 Argon (High) first at 1532 (4,900 votes), Claude Opus 5.5 (High) second at 1516, Claude Opus 5 (Max) fourth at 1509, Claude Sonnet 5.5 (xHigh) 28th at 1473, GPT-6.1 Sol (Max) 66th at 1443 and GPT-6 Astra (Max) 73rd at 1441.

Arena WebDev leaderboard: Opus 5.5 first, GPT-6 Astra second

Arena's October 19, 2026 WebDev leaderboard ranks Claude Opus 5.5 (Max) first at 1807 (2,925 votes), GPT-6 Astra (Max) second at 1774, Claude Sonnet 5.5 (xHigh) third at 1768, GPT-6.1 Sol (Max) fourth at 1753, Claude Opus 5 (Max) eighth at 1689 and Gemini 4 Argon (High) tenth at 1678.

Vals AI Terminal-Bench 4.0 with one harness: Opus 5.5 65.2%, Astra 59.6%, Argon 57.6%

Running every model in the same Mini-SWE-agent harness, Vals AI reports Claude Opus 5.5 at 65.15%, Sonnet 5.5 64.14%, GPT-6 Astra 59.60%, Gemini 4 Argon 57.58%, GPT-6.1 Sol 55.05% and Opus 5 53.53%. GPT-6.1 Sol cost $1.72 per test against $13.20 for Opus 5.5.

Opus 5 in Claude Code scores 53.9% on Terminal-Bench 4.0 at xhigh effort

Claude Code with Opus 5 scored 53.94% at xhigh, 51.82% at max (posted August 27), 50.3% at high, 44.85% at medium and 34.85% at low, each over 330 trials.

Who is affected:

Teams still on Opus 5 deciding whether to move to Opus 5.5.

What to do:

Compare against Opus 5.5 (64.85%) before upgrading.

Vals AI retires SWE-bench Verified with Opus 5 first at 97.0%

Vals AI archived its SWE-bench Verified leaderboard because performance has saturated. As of September 1, 2026, Claude Opus 5 with Mini-SWE-agent ranks first at 97.00%, ahead of DeepSeek V4 Pro 0813 (96.40%) and GPT-5.6 Sol (96.20%). Newer models such as Opus 5.5 and GPT-6 are not run.

Who is affected:

Anyone citing SWE-bench Verified to compare current models.

What to do:

Use Terminal-Bench 4.0 or SWE-Bench Pro results for newer models.