Claude

claude-sonnet-4-5-20250929 retires Nov 30, 2026. Sonnet 5.5 costs $2/$10/$0.10 cache read vs $3/$15/$0.30, but turns the same text into ~30% more tokens and rejects sampling parameters, thinking budgets, prefill and forced tool choice. Cost math and a 5-week migration plan.

Anthropic's first new API version since 2023-06-01 shipped Oct 21, 2026 with Python SDK 2.0.0, TypeScript 1.0.0 and other majors. temperature/top_p/top_k now return 400, keys go out as Authorization: Bearer, and MessageParam is a union. Here is how to fix each error.

Sonnet 5.5 costs half of Opus 5.5 per token and nearly matches it on benchmarks, but uses ~60% more output tokens — $7.67 vs $5.98 per task at max effort on Artificial Analysis v4.3.2. Benchmarks, a per-task cost worked example, and a task-by-task pick table.

Claude Sonnet 5.5 (claude-sonnet-5-5): $2/$10 per 1M tokens, cache reads $0.10 since Oct 7 (half of Opus 5.5), 1M context, 128K output. Worked cache math, Artificial Analysis's $5.46 vs $5.98 per task, Haiku 5.5, API 2026-10-21 changes and the Nov 30 Sonnet 4.5 retirement.

Claude Opus 5.5 and GPT-6 Sol launched 90 minutes apart on 22 Sept 2026. Opus 5.5 wins on benchmarks; Sol costs half per token. Pricing, cost per task, shared benchmarks, Claude Code vs Codex, and which to pick.

Migrating from Claude Opus 5 to Opus 5.5: thinking can't be disabled, forced tool_choice returns 400, thinking blocks are bound to the conversation, computer_20251124 is rejected, and effort defaults to medium. Exact errors, before/after code, costs, and a rollback plan.

Claude Opus 5.5 (claude-opus-5-5): $4/$20 per MTok, 1M context, medium default effort. Fast mode went GA on 15 Oct 2026 at $8/$40 with no beta header, on the Claude API, Foundry and Anthropic-managed Google Cloud. Benchmarks, Artificial Analysis #1 at 58 and per-effort costs.

GPT-6 Astra lists at exactly twice Claude Opus 5. On the one independent same-harness index that has run both, Opus 5 scores higher. Here is the full cost and benchmark breakdown.

GPT-6 Astra and Claude Fable 5.1 launched two days apart at identical $10/$50 pricing. We check the verified benchmarks and run the real cost arithmetic on caching and long context.

Fable 5.1 leads every head-to-head benchmark but costs 2x on list. Its cache reads are half Opus 5's, which flips the cost answer for cache-heavy agentic workloads.

Claude Fable 5.1 ships at the same $10/$50 price as Fable 5 — but cache reads drop 4x to $0.25/MTok, agentic benchmarks jump sharply, and forced tool_choice now returns a 400 error. A full head-to-head with the caching arithmetic and a clear switch/don't-switch rule.

Anthropic released Claude Fable 5.1 on 1 September 2026 at the same $10/$50 price as Fable 5. The real change is a 4x cut to cache reads, plus a breaking change to forced tool use.

Claude Opus 5 leads on independently verified coding benchmarks; Kimi K3 costs 40% less and ships open weights. A head-to-head on benchmarks, cost, context, openness and speed — with an explicit decision rule.

Meta published a benchmark chart where its own model loses to Claude Opus 5 — and independent harnesses rank Muse Spark 1.2 lower still. A close read of the launch numbers.

Claude Opus 5 launched at the same price as Opus 4.8 but posts a full generation of gains: 79.2% on SWE-bench Pro, double the agentic coding, a new effort toggle, and stronger safety. Here's what changed and why the upgrade is low-risk.

Claude Opus 5 landed July 24, 2026 as Anthropic's near-frontier default. A task-by-task guide to choosing between Sonnet 5 and Opus 5 by workload and budget, with real benchmarks, pricing, and a which-to-pick decision list.

Claude Opus 5 comes close to Fable 5's frontier intelligence at half the input price ($5 vs $10). Here's the benchmark head-to-head, the pricing breakdown, and exactly when Fable 5 is still the right call for long-horizon autonomous agents.

A hands-on guide to running Claude Opus 5 in Claude Code: how to select claude-opus-5, when to use fast mode, how effort levels work, self-verification in agent loops, and the 1M context for large repos.

A complete benchmark reference for Claude Opus 5: what Frontier-Bench, ARC-AGI-3, GDPval-AA v2, SWE-bench Pro, CursorBench, AutomationBench and OSWorld measure, Opus 5's exact score on each, the comparison models, and why capability per dollar is the real story.

Claude Opus 5 lands at $5 input / $25 output per million tokens, same as Opus 4.8 and half of Fable 5. The real cost lever is the new low/medium/high effort toggle. Here's a full pricing table, a worked cost example, and a routing strategy that can cut your AI bill ~40%.

Claude Opus 5 vs GPT-5.6 Sol, head-to-head on the public numbers: Frontier-Bench 43.3 vs 34.4, ARC-AGI-3 30.2 vs 7.8, GDPval-AA v2 1,861 vs 1,736. Benchmarks, pricing, and the honest switching-cost caveat.

Anthropic's Claude Opus 5 brings near-frontier intelligence at half the price, a low/medium/high effort toggle, and record coding benchmarks. Here's the full breakdown.

Fable 5's included-in-subscription window ends July 7, 2026. Here's exactly how usage credits work, what Fable 5 costs after the switch, and how to set spend limits so an agent doesn't drain your balance.

Anthropic's agentic mid-tier Claude Sonnet 5 vs OpenAI's flagship GPT-5.5: benchmarks, pricing, and when to use which for agents and reasoning.