Claude Opus vs Sonnet vs Haiku: Which Model in 2026?
The short answer
Opus 5.5 for long agentic coding and knowledge work, Sonnet 5 for everyday interactive tasks, Haiku 4.5 for high-volume cheap calls, and Fable 5.1 only when you need the flagship’s max-effort reliability. That is the September 2026 answer; the tier names are stable but the models behind them change every few months, so this guide anchors on the current line-up and the durable rules for choosing between tiers.
The current line-up (September 2026)
| Claude Fable 5.1 | Claude Opus 5.5 | Claude Sonnet 5 | Claude Haiku 4.5 | |
|---|---|---|---|---|
| Role | Flagship | Long-running agents, coding, knowledge work | Fast general-purpose | Fastest, cheapest |
| Released | September 3, 2026 | September 22, 2026 | GA June 30, 2026 | 2025 |
| Price (in / out per MTok) | $10 / $50 | $4 / $20 | $2 / $10 | $1 / $5 |
| Cache read | $0.25 (2.5%) | $0.20 (5%) | $0.20 (10%) | $0.10 (10%) |
| Batch API | 50% off | 50% off | 50% off | 50% off |
| Context / max output | 1M / 128K | 1M / 128K | 1M / 128K | 200K / 64K |
| Latency (Anthropic’s label) | Slower | Moderate | Fast | Fastest |
| Thinking | Adaptive, always on | Adaptive, always on | Adaptive | Extended (manual budget) |
| Default effort | high | medium | high | No effort parameter |
| Knowledge cutoff | June 2026 | June 2026 | January 2026 | February 2025 |
| Subscription access | Max, Team Premium | Pro and up | Free and up | Free and up |
| Next version | — | — | Sonnet 5.5 (weeks) | Haiku 5.5 (weeks) |
Model IDs: claude-fable-5-1, claude-opus-5-5, claude-sonnet-5, claude-haiku-4-5. All four are on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry.
How the tiers differ in practice
Fable is the model Anthropic ships with its strictest safeguards and its highest default effort. Since Opus 5.5, it no longer leads most benchmarks; Anthropic’s own table shows Opus 5.5 ahead of Fable 5.1 on every row, and Artificial Analysis scores them 58 and 53. Its remaining edge is behaviour at max effort: in independent testing Fable 5.1 produced its best results at max while Opus 5.5 at max twice exhausted its 128K output budget while still reasoning. If you run single-shot, very hard problems at max, Fable is the safer default.
Opus is the workhorse. Opus 5.5 leads agentic coding (Terminal-Bench 4.0 66.4%), knowledge work (GDPval-AA v2.1 1846 Elo) and computer use (OSWorld 2.0 81.8% partial), generates output 30% faster than Opus 5, and its $0.20 cache reads make multi-hour sessions cheap. Four of its five effort levels sit on Artificial Analysis’s intelligence-versus-cost frontier. Its default effort is medium, which is where the 40% cost saving versus Opus 5 lives.
Sonnet is the tier most applications should start with. Same 1M context and 128K output as Opus, half the price, lower latency, and a permanent $2/$10 price after Anthropic cancelled the planned September 2026 rise. What you give up: a January 2026 knowledge cutoff (five months behind Opus 5.5), and lower scores on long-horizon agent benchmarks. Anthropic’s Sonnet 5.5, promised for the coming weeks, is expected to carry over Opus 5.5’s efficiency and writing improvements.
Haiku is for volume. Haiku 4.5 is the fastest model, costs $1/$5, and works well as a sub-agent, classifier or router. It is also the most dated: 200K context, 64K output, February 2025 cutoff, no adaptive thinking. Competitively it is under pressure from GPT-6 Luna at $0.10/$0.50; Haiku 5.5 is the response to watch.
Routing table
| Task | Model | Effort | Why |
|---|---|---|---|
| Multi-hour coding agent, migrations, audits | Opus 5.5 | medium–high | Terminal-Bench 4.0 66.4%; 200K-line audit in <3h |
| Claude Code daily driver | Opus 5.5 | medium | Default; GitHub measured fewest steps and tokens |
| Interactive editing, PR-sized changes | Sonnet 5 | high (default) | Half the price, lower latency, same context |
| Reports, financial models, decks | Opus 5.5 | medium | GDPval leader; 16/18 fact-checked reports passed |
| Customer-facing chat | Sonnet 5 | medium | Fast, cheap, 1M context for long threads |
| Classification, extraction, routing, moderation | Haiku 4.5 | — | $1/$5, fastest; batch for 50% off |
| Sub-agents inside an Opus workflow | Haiku 4.5 or Sonnet 5 | — / low | Keep the expensive model for planning |
| Hardest single-shot reasoning at max | Fable 5.1 | max | Did not over-think to failure |
| Whole-repository prompts (>272K tokens) | Opus 5.5 or Sonnet 5 | — | No long-context surcharge, unlike GPT-6 |
| Offensive security, biology R&D | Whichever your verification tier allows | — | Fable and Opus 5.5 gate these behind programs |
Durable rules for choosing a tier
- Route by task length, not task difficulty. A hard question answered in one turn is a Sonnet job; a medium-difficulty task that takes 200 tool calls is an Opus job, because per-step reliability compounds.
- Price the cached tokens, not the list price. On agent loops 90%+ of input is cached. Opus 5.5’s $0.20 cache read is the same as Sonnet 5’s, so the real gap between them on long sessions is closer to 2x on output than the headline suggests.
- Check the knowledge cutoff for API-heavy coding. A model that predates the library version you use will hallucinate signatures. Sonnet 5’s January 2026 cutoff is the one to watch here.
- Start one tier down and escalate on failure. Sonnet with an Opus fallback triggered by failed tests or low confidence usually beats Opus everywhere at a fraction of the cost.
- Re-run your effort sweep on every new model. Defaults change (Opus 5 defaulted to high, Opus 5.5 to medium) and tokens-per-effort change with them.
- Expect the tiers to shift. Anthropic has cut Opus prices once (Opus 5.5) and made a Sonnet increase disappear in 2026; Sonnet 5.5 and Haiku 5.5 will reshuffle this table within weeks. Anchor decisions on measured cost per task on your own workload.
For the latest Opus specifically, see What is Claude Opus 5.5?; for how the tiers compare with OpenAI’s, see GPT-6 Sol vs Luna vs Astra.
Last verified: September 23, 2026.