Claude Opus 4.6 vs GPT-5.1

Summary of test-by-test outcomes in our 12-test suite (scores are our 1–5 internal ratings unless noted):

• Tool calling: Claude Opus 4.6 scores 5 vs GPT-5.1 4 — Opus is tied for 1st ("tied for 1st with 16 other models out of 54 tested"), which translates to more accurate function selection, argument filling and sequencing for multi-step agents.
• Safety calibration: Opus 5 vs GPT-5.1 2 — Opus is tied for 1st with 4 others; GPT-5.1 ranks 12 of 55. This means Opus better refuses harmful prompts while permitting legitimate ones in our tests.
• Agentic planning: Opus 5 vs GPT-5.1 4 — Opus tied for 1st (with 14 others); it better decomposes goals and plans recovery paths in our scenarios.
• Creative problem solving: Opus 5 vs GPT-5.1 4 — Opus tied for 1st (with 7 others), giving stronger non-obvious feasible ideas.
• Constrained rewriting: GPT-5.1 4 vs Opus 3 — GPT-5.1 ranks 6 of 53 while Opus ranks 31 of 53; GPT-5.1 is clearly better when compressing text to strict character limits.
• Classification: GPT-5.1 4 vs Opus 3 — GPT-5.1 tied for 1st (with 29 others) while Opus ranks 31 of 53; expect fewer routing/mapping errors with GPT-5.1 in our tests.
• Structured output, strategic analysis, faithfulness, long context, persona consistency, multilingual: ties across both models (scores equal); e.g., both score 4 on structured_output and 5 on long_context and faithfulness, with Opus and GPT-5.1 each tied for 1st in long_context and faithfulness. External third-party context (Epoch AI): on SWE-bench Verified Opus scores 78.7 (rank 1 of 12) vs GPT-5.1 68 (rank 7 of 12); on AIME 2025 Opus 94.4 (rank 4 of 23) vs GPT-5.1 88.6 (rank 7 of 23). We present those Epoch AI numbers as supplementary evidence that Opus leads on coding and advanced math benchmarks, while our internal suite highlights where GPT-5.1 retains advantages (constrained rewriting, classification).

Pricing (per mTok = per 1,000 tokens) is: Claude Opus 4.6 input $5 / output $25; GPT-5.1 input $1.25 / output $10. Using a 50/50 input/output split as a simple practical scenario: for 1M tokens/month Opus ≈ $15,000 vs GPT-5.1 ≈ $5,625; for 10M tokens Opus ≈ $150,000 vs GPT-5.1 ≈ $56,250; for 100M tokens Opus ≈ $1,500,000 vs GPT-5.1 ≈ $562,500. The upshot: at scale (millions of tokens/month) GPT-5.1 reduces bills by roughly two- to three-fold in typical input/output mixes; product teams, startups, and high-volume APIs should care most about the gap, while organizations prioritizing agent safety, long-running workflows, and top tool-calling quality may justify Opus’s premium.

Choose Claude Opus 4.6 if you need top-tier tool calling, strict safety calibration, agentic planning, long-context workflows, or the strongest coding and math performance (Opus scores 5/5 on tool_calling and safety_calibration; 78.7% on SWE-bench Verified, Epoch AI). Choose GPT-5.1 if budget and per-token cost are critical, or if your primary needs are classification and constrained rewriting (GPT-5.1 scores 4/5 on both) — it costs $1.25/$10 per mTok vs Opus $5/$25 per mTok and reduces monthly spend materially at scale.