Claude Sonnet 5, Explained: Pricing, the New Tokenizer, 1M Context, and Opus 4.8

Sonnet 5 in 60 seconds

• What it is: Anthropic’s new mid-tier model (API ID claude-sonnet-5), launched June 30, 2026 as “our most agentic Sonnet yet.”
• Price: $2/$10 per million input/output tokens through August 31, then $3/$15 — the same headline rate as Sonnet 4.6.
• Context: native 1M-token window, up to 128K output tokens, adaptive thinking on by default.
• The catch: a new tokenizer maps the same text to ~1.0–1.35x more tokens. At the standard rate that is a real per-task price rise the sticker doesn’t show.
• Benchmarks (Anthropic’s figures): beats Opus 4.8 on Terminal-Bench 2.1 (80.4% vs 74.6%), trails it on SWE-bench Pro (63.2% vs 69.2%).
• Where: default on Free/Pro, available to Max/Team/Enterprise, and the default model in Claude Code from v2.1.197.

What changed versus Sonnet 4.6

Sonnet 5 is the successor to Sonnet 4.6 (which shipped in February 2026), and Anthropic positions it as a jump on agentic work — planning, tool use, running autonomously — rather than a general facelift. From the launch announcement: “Sonnet 5 narrows the gap: its performance is close to that of Opus 4.8, but at lower prices.” The concrete deltas versus 4.6, all from Anthropic’s system card:

• SWE-bench Pro: 63.2% vs 58.1% — harder, multi-file real-world coding tasks.
• Terminal-Bench 2.1: 80.4% vs 67.0% — the biggest jump, on real terminal/command-line work.
• FrontierCode v1: 38.8% vs 15.1% — more than doubled on the hardest coding eval Anthropic reports.
• Context window: native 1M tokens (Sonnet 4.6 shipped without a 1M default in Claude Code).
• Tokenizer: rebuilt — the same text now maps to more tokens. This is the change nobody put on a slide.

The honest one-liner: Sonnet 5 is a real capability upgrade over 4.6 on agentic and coding work, priced identically per token at standard rates but not per task, because of the tokenizer. Hold that tension — it’s the whole story of this launch.

The five named pieces

Five things carry the launch. Each gets a deep dive below; this is the map.

1. Pricing — $2/$10 promo through Aug 31, then $3/$15. Identical headline rate to Sonnet 4.6.
2. The 1M context window — native, in the API and in Claude Code, not a paid add-on tier.
3. The new tokenizer — the same text is ~1.0–1.35x more tokens. The centerpiece, because it quietly rewrites the pricing.
4. The benchmarks — close to Opus 4.8, ahead of it on Terminal-Bench, behind on SWE-bench Pro.
5. Where you get it — default on Free/Pro/Claude Code, plus the claude-sonnet-5 API for everyone else.

How to select Sonnet 5 in Claude Code

The Claude Code v2.1.197 changelog entry, verbatim: “Introducing Claude Sonnet 5: now the default model in Claude Code, with a native 1M-token context window and promotional pricing of $2/$10 per Mtok through August 31. Update to version 2.1.197 for access.” So the fastest path is simply to update — a fresh session is already on Sonnet 5.

# 0. Update first — Sonnet 5 needs Claude Code v2.1.197+
claude update

# 1. It's already the default after updating. To set it
#    explicitly in a session:
/model sonnet          # 'sonnet' now resolves to Sonnet 5

# 2. At startup, this session only:
claude --model sonnet

# 3. Environment variable, this terminal only:
export ANTHROPIC_MODEL=sonnet

# 4. Settings file — ~/.claude/settings.json
{
  "model": "sonnet"
}

Two things worth knowing. The sonnet alias tracks the recommended Sonnet version, so it points at Sonnet 5 now; pin the exact ID with claude-sonnet-5 if you need a fixed target across a team. And because Sonnet 5 is the default, the more common question on r/ClaudeCode after launch was the inverse — how to go back to Opus 4.8 for a specific job: /model opus. Model routing is now a per-task decision; if you want the full playbook for switching between tiers, we wrote it up in the Claude Code model-routing guide.

The tokenizer pricing math (the part nobody advertised)

This is the most important section in the post, so it gets real numbers. Anthropic’s own note on the launch page: “The same input can map to more tokens: roughly 1.0–1.35x depending on the content type.” Sonnet 5 uses a rebuilt tokenizer — the component that chops your text into billable tokens — and it is less efficient on most content than the one Sonnet 4.6 used.

Simon Willison ran his own token counter on real documents the day it launched and found “the same input text produces approximately 30% more tokens than on Claude Sonnet 4.6,” with a language-dependent spread: roughly 1.4x for English prose, 1.33x for Spanish, 1.28x for Python code, and negligible change for Simplified Mandarin. Different content, different tax.

Why it matters: standard pricing ($3/$15 per million) is identical to Sonnet 4.6’s per-token rate. So the price card looks flat. But you are billed per token, and the same job is now more tokens. Worked example — a task that measured 100,000 input and 20,000 output tokens on Sonnet 4.6, inflated by 1.35x on the new tokenizer:

Read the last row left to right. Through August 31 the promo rate more than offsets the tokenizer tax — the task is ~10% cheaper than it was on 4.6. From September 1, the same task on the same standard rate costs ~35% more, purely because of how the text is counted. The promo window is, in effect, hiding the increase until it ends.

Benchmarks, read honestly

All figures below are Anthropic’s own, published in the Claude Sonnet 5 system card dated June 30, 2026, and on the launch page. Treat them as vendor-reported, not independent.

Against its own family (launch-page chart): Sonnet 5 lands close to Opus 4.8, ahead on some evals, behind on others.

• SWE-bench Pro (agentic coding): Sonnet 5 63.2%, Opus 4.8 69.2%, Sonnet 4.6 58.1%. Opus 4.8 still wins the hardest coding.
• Terminal-Bench 2.1: Sonnet 5 80.4%, Opus 4.8 74.6%, Sonnet 4.6 67.0%. This is the eval where the mid-tier model beats the flagship.
• SWE-bench Verified: Sonnet 5 85.2% (Anthropic’s reported figure for the classic 500-problem set).

Against competitors (system-card table): Anthropic’s own summary table compares Sonnet 5 to Sonnet 4.6, GPT-5.5, and Gemini 3.5 Flash — and here is the detail the marketing skips. On Terminal-Bench 2.1, GPT-5.5 via Codex CLI scores 83.4%, ahead of Sonnet 5’s 80.4%. So “beats the flagship” is an in-family claim; across vendors, a competitor still edges terminal work. Sonnet 5 does lead that table on SWE-bench Pro (63.2 vs GPT-5.5’s 58.6), FrontierCode v1 (38.8 vs 25.5), and GDPval-AA v2 (1618 Elo vs 1509). If you run agents across models, the GPT-5.5-on-Codex line is worth your own head-to-head — see Claude Code vs Codex CLI.

One more caveat, courtesy of the community: Anthropic quietly swapped a benchmark chart on launch day (covered in the community section). Vendor benchmarks are a starting point for a shortlist, never a finished decision. For a cross-vendor take on which coding model to actually pick, see the best AI coding model in 2026 — how Sonnet 5 stacks up against GPT-5.6 and GLM-5.2.

The 1M context window

Sonnet 5 ships a native 1 million-token context window and up to 128,000 output tokens, per the system card and the Claude Code changelog. “Native” matters: it is the standard configuration in the API and in Claude Code, not a separate 1M tier you opt into and pay a surcharge for. For agentic work — long autonomous sessions that read a lot of a codebase before acting — a 1M window is the difference between compacting context every few turns and keeping the whole task in view.

Anthropic pushed it further in one eval: its BrowseComp agentic search test used a 10M-token limit with context compaction — automatic summarization of older context — that triggers at 200k. That is an evaluation configuration, not the default you get; the number to plan around is 1M. The practical read: with a 1M window and the lower promo price, Sonnet 5 is priced for exactly the long-horizon agent loops that used to force you onto a more expensive model. That is the whole pitch.

What surprised us

Three things we assumed going in that the sources corrected:

• We assumed “same price as 4.6” meant cost-neutral. It doesn’t. Standard per-token rates match, but the tokenizer means the same task bills more tokens. The promo masks it until September 1. We nearly wrote “free upgrade” before doing the math above.
• We assumed Sonnet 5 beat Opus 4.8 on coding generally. It doesn’t — Opus 4.8 still leads SWE-bench Pro (69.2 vs 63.2). Sonnet 5’s win is specifically Terminal-Bench, plus “close enough” across the board at a lower price. “Close to Opus” is the accurate framing, not “better.”
• We assumed the “beats the flagship” Terminal-Bench line was unambiguous. Within Anthropic’s family it is. But the same system card shows GPT-5.5 on Codex CLI scoring higher (83.4). The flagship it beats is Anthropic’s flagship.

Who it’s for (and who should stay on Opus 4.8)

Sonnet 5 is now the sensible default for most work. The decision is really about the few cases where it isn’t.

Community signal

The launch tweet above is the first-party framing. The developer reaction on r/ClaudeAI split three ways: genuine enthusiasm for the concision, sharp skepticism about a launch-day benchmark chart swap, and a cost worry pointed straight at the tokenizer.

The upside people actually cared about was Sonnet 5 doing the job with less talk. The top comment on the launch thread (2,700+ upvotes on the post):

The skepticism was aimed at Anthropic’s own charts. Within hours, a 1,000-upvote thread caught Anthropic replacing the BrowseComp cost-performance chart. Anthropic’s own erratum, quoted in the thread: “In the original version of this post, we included a cost-performance chart for the BrowseComp evaluation that was based on data from a simpler methodology… This had the result of underestimating Sonnet 5’s performance.” The community read was less charitable:

The cost worry tied directly back to the tokenizer. On the “Sonnet 5 vs 4.6” thread, the practical fear was blunt — and one contrarian took a harder line, arguing Anthropic’s mid-tier has fallen behind cheaper open-weight competition:

That is the fault line across every thread we read: the capability is respected, the pricing-through-tokenization is resented. Both can be true.

Verdict

Frequently asked questions

Glossary

• Claude Sonnet 5 — Anthropic’s mid-tier model (API ID claude-sonnet-5), launched June 30, 2026.
• Tokenizer — the component that splits text into billable tokens. Sonnet 5’s is rebuilt and less efficient on most content.
• Context window — how much text the model can hold at once. Sonnet 5: 1M tokens native.
• Output tokens — the model’s generated text, billed at the higher rate. Sonnet 5 caps at 128K.
• Adaptive thinking — the model deciding per step how much to reason; on by default in Sonnet 5.
• Context compaction — automatic summarization of older context so a long session stays under the window limit.
• SWE-bench Pro — a hard coding benchmark of multi-file, real-repository tasks. Sonnet 5: 63.2%.
• Terminal-Bench 2.1 — benchmark for real command-line/terminal tasks. Sonnet 5: 80.4%.
• Model alias — a short name (sonnet, opus, haiku) that resolves to the recommended version; sonnet now points at Sonnet 5.
• Promotional pricing — the discounted $2/$10 launch rate, in effect through August 31, 2026.

Sources

Primary

• anthropic.com/news/claude-sonnet-5 — launch announcement; pricing, availability, tokenizer note (“roughly 1.0–1.35x”), “close to Opus 4.8” framing.
• anthropic.com/claude-sonnet-5-system-card — benchmark table (SWE-bench Pro 63.2, Terminal-Bench 2.1 80.4, GPT-5.5 Codex CLI 83.4, GDPval-AA v2 1618), 1M/128K configuration.
• code.claude.com/docs/en/changelog — v2.1.197 entry: default model in Claude Code, native 1M context, $2/$10 through August 31.
• @claudeai launch post — first-party announcement, June 30, 2026.

Community & contrarian

• r/ClaudeAI — Introducing Claude Sonnet 5 — launch reaction; the “a third of the output” concision take.
• r/ClaudeAI — Anthropic quietly updated the benchmark chart — the launch-day BrowseComp chart swap and the erratum.
• r/ClaudeAI — Sonnet 5 vs 4.6 on arena.ai — tokenizer cost worry; the GLM 5.2 cost-per-capability argument.
• simonwillison.net — What’s new in Claude Sonnet 5 — independent token-counting (~30% more tokens), 1M/128K, sampling-parameter changes.
• TechCrunch — Claude Sonnet 5 launch coverage — agentic-coding figures (63.2 / 69.2 / 58.1), pricing context vs GPT-5.5 and Gemini.

Internal

• /blog/best-ai-coding-model-2026 — Sonnet 5 vs GPT-5.6 vs GLM-5.2
• /blog/fable-5-claude-code-model-routing-guide-2026 — routing between model tiers
• /blog/claude-code-vs-codex-cli-2026 — the GPT-5.5-on-Codex angle
• /clients/claude-code
• /servers — browse MCP servers