Anthropic

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.

Claude Sonnet 5.5 and GPT-6.1 Sol launched a day apart at the same $2/$10 price. Sonnet leads Artificial Analysis's Intelligence Index v4.3.2 56.00 to 51.83; Sol costs $0.72 per task vs $7.67. Benchmarks, caching, long-context pricing and a worked cost example.

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.

Opus 5.5 leads AA at 58 ($5.98/task; 54 for $1.82 at high). Gemini 4 Argon (53, $1.62) wins DeepSWE v1.1 77.9% but trails Terminal-Bench 4.0 57.4% vs 66.4%, and doubles to $4/$20 on Dec 1. Astra $10/$50, Grok 4.7 $2/$6 at 46.

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 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 most agentic Sonnet yet, launched June 30, 2026. Full benchmark table, real pricing (including the tokenizer catch), availability, and honest verdicts vs Sonnet 4.6, Opus 4.8, GPT-5.5 and Gemini.

A practical 2026 guide to how Claude Code usage limits actually work and the concrete habits that get more done inside them: right model per task, context hygiene, a tight CLAUDE.md, and when an API key beats a subscription.

Claude Fable 5 is back online as of July 1, 2026, after the U.S. lifted its export-control order. Here's what changed, how Anthropic brought it back, and how to access it.

Anthropic's first publicly available Mythos-class model, released June 9, 2026. Third-party benchmarks, pricing, context window, availability, the safety reroute to Opus 4.8, and how it compares to GPT-5.5 and Gemini 3.5.