Anthropic Launches Claude Sonnet 5.5: Over 30% Faster, Up to 30% Cheaper
On September 29, Anthropic officially launched Claude Sonnet 5.5, the second model in the Claude 5.5 family, with the product page appearing online — Reddit users spotted it before the announcement. Positioned as a faster, cheaper daily-workhorse model alongside Opus 5.5, it is a clear upgrade over Sonnet 5, and it is already available on the Claude platform and in Claude Code.
Confirmed
- Over 30% faster than Sonnet 5, the fastest Sonnet yet; cost per task down up to 30% for most tasks (same pricing, fewer tokens per task).
- Pricing unchanged from Sonnet 5: $2/$10 per million tokens (input/output), $0.20 cache reads; adaptive thinking on by default.
- Terminal-Bench 4.0 jumped from 10.3% to 70.6%.
- Anthropic granted a one-time usage limit reset last Tuesday for all Pro, Max and Team users, usable until October 22.
- A high-concurrency variant exists in the family; Haiku 5.5 arrives in the coming weeks.
- Official guidance: start large projects with Opus; use Sonnet for balanced quality/speed/cost. Claude app defaults to medium effort, Platform API to high.
- Preserved thinking extends to Sonnet 5.5: thinking blocks are tied to the originating organization, and switching accounts mid-session forces a session re-read to curb cross-account distillation attacks.
- The launch post includes a developer guide covering model selection, migration, and use in Claude Code.
Early experiments
- @repete generated fall-leaf simulators with Sonnet 5 vs 5.5 for direct comparison; @forwardeditor ran identical-prompt ball-physics simulations; @LEJlimited turned a 60×46-pixel emoji into a 3D-printable model printed within hours.
Why it matters
Faster output and lower effective cost at unchanged prices make Sonnet 5.5 a strong default for everyday engineering and content tasks, intensifying mid-tier model competition; the Terminal-Bench leap signals a step change in terminal/agent capability. Preserved thinking is a notable engineering measure against distillation attacks.
2026-09-29 ~ 2026-09-29 · 58 related posts
- Episode 1: Insiders claim OpenAI and Anthropic hold models far ahead of public releases(2026-09-24, 2 posts)
- Episode 2: Anthropic Reportedly Set to Ship Sonnet/Haiku 5.5 Ahead of OpenAI DevDay(2026-09-26, 2 posts)
- Episode 3: Claude Sonnet 5.5 leak: gradual rollout underway, launch imminent(2026-09-27, 20 posts)
- Episode 4: Insider Claims OpenAI Is Sitting on a Stronger Model(2026-09-28, 2 posts)
- Episode 5: Rumors: Anthropic Ships Opus 5.5 and Sonnet 5.5 Ahead of OpenAI DevDay(2026-09-29, 7 posts)
- Episode 6: Anthropic Launches Claude Sonnet 5.5: Over 30% Faster, Up to 30% Cheaper(2026-09-29, 58 posts)
- Episode 7: Claude Sonnet 5.5 launches near-flagship intelligence amid token-cost controversy(2026-09-29, 27 posts)
- Episode 8: Multiple leaks claim Claude Sonnet 5.5 decisively outscores GPT-6 sol(2026-09-29, 5 posts)
- Episode 9: Data comparison sparks debate: Sonnet 5.5 called a flop, GPT-6 Sol wins on value(2026-09-29, 2 posts)
- Episode 10: Sonnet 5.5 Nearly Matches Flagship Opus in Real-World Use(2026-09-29, 3 posts)
Primary sources
- Anthropic launches Claude Sonnet 5.5: 30% faster and up to 30% cheaper than Sonnet 5 — AnthropicAI ·
- Anthropic launches Claude Sonnet 5.5: 30% faster than Sonnet 5 at the same $2/$10 pricing — ClaudeDevs ·
- Claude Sonnet 5.5 jumps from 10.3% to 70.6% on Terminal-Bench 4.0, runs 30% faster at same price — claudeai ·
- Claude Sonnet 5.5 quietly goes live on Anthropic's official page — Ok_Barracuda_1161 · 2026-09-29
- Anthropic launches Claude Sonnet 5.5: 30%+ faster, up to 30% cheaper for most work — claudeai · 2026-09-29
- [source] Claude Sonnet 5.5 jumps from 10.3% to 70.6% on Terminal-Bench 4.0, runs 30% faster at same price — claudeai · 2026-09-29
- [source] Anthropic launches Claude Sonnet 5.5: 30% faster and up to 30% cheaper than Sonnet 5 — AnthropicAI · 2026-09-29
- Anthropic's Addy Osmani on Sonnet 5.5: built for well-scoped everyday tasks — addyosmani · 2026-09-29
- Anthropic's Alex Albert praises Sonnet 5.5: fast, clear, big jump over Sonnet 5 — alexalbert__ · 2026-09-29
- Anthropic ships Claude Sonnet 5.5: 30%+ faster than Sonnet 5, up to 30% cheaper — jarrodwatts · 2026-09-29
- Claude Sonnet 5.5 released: near Opus 5.5 performance at half the price — ross2000 · 2026-09-29
- Sonnet 5.5 keeps $2/$10 per million tokens; thinking always on, `between_tools` disables it — ClaudeDevs · 2026-09-29
- Anthropic extends preserved thinking to Sonnet 5.5 to curb account-switching distillation attacks — ClaudeDevs · 2026-09-29
- Anthropic's guidance: start with Opus for large projects; max-effort Sonnet loses its balance — ClaudeDevs · 2026-09-29
- Sonnet 5.5 live for all; Pro/Max/Team users can claim a usage reset before Oct 22 — ClaudeDevs · 2026-09-29
- Claude Sonnet 5.5 lands in Claude Code: 30% faster, up to 20% lower platform costs — lydiahallie · 2026-09-29
- Sonnet 5.5 cuts per-task cost up to 30%, commentators say OpenAI is cornered — kimmonismus · 2026-09-29
- Anthropic launches Sonnet 5.5: 30% faster and up to 30% cheaper than Sonnet 5 — felixrieseberg · 2026-09-29
- Anthropic ships Claude Sonnet 5.5: half of Opus 5.5's price, matches it on most benchmarks — AGI Hunt · 2026-09-29
- Could an Opus orchestrator with Sonnet workers cut coding agent costs? — YashasGunderia · 2026-09-29
- [source] Anthropic launches Claude Sonnet 5.5: 30% faster than Sonnet 5 at the same $2/$10 pricing — ClaudeDevs · 2026-09-29
- Anthropic: start big projects with Opus, use Sonnet 5.5 for balanced everyday tasks — ClaudeDevs · 2026-09-29
- Anthropic's preserved thinking blocks account-switching distillation attacks — ClaudeDevs · 2026-09-29
- Claude Sonnet 5.5 Is Now Available, Devs Say "Claude Is So Back" — daniel_mac8 · 2026-09-29
- Anthropic ships Claude Sonnet 5.5: 30% faster, 70.6% on Terminal-Bench 4.0 — petrusenko_max · 2026-09-29
- Claude Sonnet 5.5 lands in Rork, generating output over 30% faster than Sonnet 5 — rudrank · 2026-09-29
- Anthropic launches Claude Sonnet 5.5: 30% faster, up to 30% cheaper, 70.6% on Terminal-Bench — addyosmani · 2026-09-29
- Anthropic's Thariq: Sonnet 5.5 makes high-abstraction agent workflows affordable — kimmonismus · 2026-09-29
- Sonnet 5.5's lower price makes token-heavy agent workflows affordable, says Every — every · 2026-09-29
- Sonnet 5.5 arrives: near-Opus coding quality at a fraction of the cost — gethackteam · 2026-09-29
- Sonnet 5.5 launches: 30% faster and up to 30% cheaper for most workloads — every · 2026-09-29
- Anthropic showcases early Sonnet 5.5 experiments, comparing fall foliage demo vs Sonnet 5 — claudeai · 2026-09-29
- Claude Sonnet 5.5 turns a 60×46 pixel emoji into a printable 3D model in hours — claudeai · 2026-09-29
- Sonnet 5.5 vs Sonnet 5: bouncing-ball physics tests from the same prompt — claudeai · 2026-09-29
- Claude official tweet shows Sonnet 5 vs Sonnet 5.5 side-by-side demo, hinting at launch — EricBuess · 2026-09-29
- Early Claude Sonnet 5.5 experiments emerge, first side-by-side vs Sonnet 5 — haider1 · 2026-09-29
- Early Claude Sonnet 5.5 experiments emerge, incl. foliage sim vs Sonnet 5 — minchoi · 2026-09-29
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